Hallow means " to Make something holy or have great respect for something" SO Hallow could refere to the Horcruxes.
Known plot details are :
* Harry returns to the home of his non-magical (Muggle) relatives, the Dursleys, during the summer. The magical protection which Albus Dumbledore arranged, that requires Harry to have a home with his surviving family, is set to expire on Harry's 17th birthday July 31.HP6
* Harry comes of age (for wizards) when he turns 17, and is therefore entitled to perform magic outside of school and to obtain a licence to Apparate. His friends Ron Weasley and Hermione Granger, and many of his classmates, already turned 17 during the sixth year, and Neville Longbottom turns 17 on July 30th — one day before Harry.4
* Harry plans to visit Godric's Hollow, and Ron Weasley and Hermione Granger plan on accompanying him on this trip, providing the jumping off point from where they will start the search to destroy the remaining Horcruxes.HP6
* There is expected to be a continuing relationship between Ginny Weasley and Harry Potter, even though Harry told Ginny in the last chapter of the sixth book that he "can't be involved with her anymore" and that they have "got to stop seeing each other" and that they "can't be together", because he's "got things to do alone now". HP6
* Hogwarts is expected to have a new head teacher or headmaster, as the previous headmaster, Albus Dumbledore, was killed.HP6
* New instructors will assume the posts for Defence Against the Dark Arts (replacing Severus Snape), and possibly Transfiguration in the event Minerva McGonagall becomes Headmistress. There may also be new Heads of Gryffindor House and Slytherin House. Horace Slughorn is the most likely candidate for head of Slytherin House. Rubeus Hagrid is also possible for Gryffindor. If Minerva McGonagall becomes headmistress a new deputy headmaster or deputy headmistress will have to be appointed. HP6
* If Harry returns to Hogwarts, it will be his seventh and final year. However, at the end of Book 6, Harry stated that he would not return even if Hogwarts were to re-open. Ron and Hermione said that they would leave Hogwarts as well, to help Harry fight Voldemort. Should Hogwarts reopen, Harry and his classmates would be expected to complete their final N.E.W.T. exams.
* Deathly Hallows is expected to identify the mysterious R.A.B., who claimed to have stolen one of Voldemort's Horcruxes with the intent to destroy it, while replacing it with a fake that was recovered by Harry and Dumbledore. In an interview, J. K. Rowling said that Regulus Black was "a fine guess" for R.A.B.'s identity. 5
* Kreacher, the former Black Family house elf which passed to Harry's ownership with the death of Sirius Black, may make an appearance. Rowling told the filmmakers of Order of the Phoenix to include the character in the movie, because he is "very important". 6
* Rowling stated on her web site that there is something "significant—even crucial" about the answer to the question of why Dumbledore had James Potter's Invisibility Cloak. 7
* Bill Weasley and Fleur Delacour plan on getting married in August. HP6
Interesting and important facts:
* We will learn something very important about Lily in Deathly Hallows:
Now, the important thing about Harry's mother - the really, really significant thing - you're going to find out in two parts. You'll find out a lot more about her in book five, or you'll find out something very significant about her in book five, and you'll find out something incredibly important about her in book seven." – J. K. Rowling13
* Rowling has long said that Harry's eyes resembling his mother's is important.14
* Severus Snape has been an important and enigmatic character throughout the books, as his true loyalty has always remained unclear. It is to be anticipated that as a surviving major character, his loyalty will be settled in the final confrontation of the book.15
Questioner: There’s an important kind of redemptive pattern to Snape.
Rowling: He, um, there’s so much I wish I could say to you, and I can't because it would ruin. I promise you, whoever asked that question, can I just say to you that I'm slightly stunned that you've said that and you'll find out why I'm so stunned if you read Book Seven. That's all I’m going to say.13
* She has stated we will learn more about Peter Pettigrew, Dumbledore, and his family.12
* At the Edinburgh book festival, Rowling mentioned that something more would be revealed about Petunia Dursley. Nothing of note occurred in book 6, so this remains to be discovered.16
"..there is a little bit more to Aunt Petunia than meets the eye...She is not a squib, although that is a very good guess. Oh, I am giving a lot away here. I am being shockingly indiscreet."
Rowling repeated this comment at the Radio city charity reading in August 2006. 17
* Whether related or not, Rowling has also said that some non-magical character will perform magic late in life in desperate circumstances.18 However, she has also said that Aunt Petunia will not perform magic.19
* Also at Edinburgh, Rita Skeeter was mentioned: "She is loathsome . . . but I can't help admiring her toughness. . . . There is more to come on Rita"16
* On Dolores Umbridge, "It's too much fun to torture her not to have another little bit more before I finish"12
* Viktor Krum is set for a reappearance.20
* The two-way mirror given to Harry by Sirius Black and his flying motorbike will return.20 Rowling refused to comment whether Sirius himself might in some way reappear, but she has also said that there was a reason why he had to die.
* Dumbledore was said to have a "gleam of triumph" in his eyes when told that Voldemort had restored his body using Harry's blood, at the end of Goblet of Fire (Ch. 36). Rowling has confirmed that this is "still enormously significant".21
* Someone from Harry's class, not Harry, Ron, or Hermione, also not who most readers would expect, will become a Hogwarts teacher. This seems to indicate that Hogwarts will indeed re-open, though possibly not until after the main events of Deathly Hallows have occurred. 13
* In an interview after the completion of the Prisoner of Azkaban film, she commented that director Alfonso Cuarón had "put things in the film that, without knowing it, foreshadow things that are going to happen in the final two books. So I really got goosebumps when I saw a couple of those things, and I thought people are going to look back on the film and think those were put in deliberately as clues."22
* There are indications that at least two of the main characters will die. In a June 2006 interview about the previously-written ending, Rowling stated that:
o "One character got a reprieve, but I have to say two die that I didn't intend to die...A price has to be paid. We are dealing with pure evil...They go for the main characters, or I do".23
* When further questioned in June 2006 about authors who kill off their main characters, Rowling said "I can completely understand, however, the mentality of an author who thinks, well, I'm going to kill them off because that means there can be no non-author-written sequels'".23
* Rowling clarified that "Dumbledore is definitely dead", when asked by Salman Rushdie and others at Radio City Music Hall in New York City. Rowling answered the same question three times, each time with increasing conviction.24.
* When asked what questions she should have been asked, she admitted that "the final book contains a couple of pieces of information that I don't think you could guess at", and declined to explain further.17 On September 13, 2006 she updated her website saying that when she was asked that question, her mind went blank. Since she couldn't make amends, she created a NAQ section of her website, in tribute to the girl who asked the question. In her NAQ section, she states:
o "Why did Dumbledore have James' invisibility cloak at the time of James' death, given that Dumbledore could make himself invisible without a cloak?"
o September 29, 2006, she reveals that Severus Snape was not under the cloak the night of the Potters' death in the Rumors Section.
* Asked which five of her characters she would like to invite to dinner, she chose Harry, Hermione and Ron, but then hesitated before choosing her last characters, saying "See... I know who's actually dead", unsure whether she was permitted to invite those who are 'dead'. 17
* Lord Voldemort was voted best villain at the Big Bad Read poll. Responding to the news Rowling commented:
o "I hope those of you who voted for him in the big bad read enjoy reading about him in book seven, where he finally gets the leg room for which he has been aching all those years in exile."25
* At their appearance in New York City on August 1, 2006, authors John Irving and Stephen King joined Rowling at a charity benefit. While there the two famous authors came together to ask Rowling NOT to kill off Harry Potter in her final book, with Irving saying, "I'll keep my fingers crossed for Harry." 1
Bill: Yes, JKR said it's called Harry Potter and the Deathly Hallows.