1.) A single part of something.
2.) As noted a bathing suit type for women.
3.) More commonly defined here it's an anime show that came from a manga from Japan. It was written by Eichiro Oda out of a love for pirates and especially the pirate Blackbeard. (Oda stated that Blackbeard was his favorite pirate) One Piece is a lot like other anime shows in that because the manga remains ongoing and continuous, the people in charge of the TV show have to keep things interesting and add contents to delay the show's progression.
The show stars Monkey D. Luffy and his pirate band. Luffy, influenced by the notoriously famous red-haired pirate Captain Shanks, decides to set sail for the Grand Line to find One Piece, a treasure hidden by Gol D. Roger before the Navy hung him from the gallows. He builds up a crew consisting of Roronoa Zolo (skilled samurai swordsmen), Nami (expert navigator and petty thief), Sanji (magnificent chef; master of fighting with his feet since he needs his hands clean for cooking), Usopp (long-nosed liar and 2nd in command), Tony Tony Chopper (silly talking reindeer who works as the crew's doctor) & Nico Robin (Assassin Girl who kicks serious ass).
An interesting thing about One Piece is there are no power levels and so most, if not all, of the characters get many significant fights. Besides Luffy's crew various other pirates threaten the seas in their goal to find One Piece or get a huge bounty on their head. (Or Both) The navy also appears and various leaders such as Chaser, Hina and Django hunt Luffy's crew and the other sea raiders down.
1.) May I have one piece of that pie?
3.) One Piece is an anime show where practically all the characters have cool powers and engage in fights often. They all have interesting moves including, but not limited too, creating copies of body parts to slap or punch people from a distance, turning large, slashing a sword so fast that shockwaves emanate from the blade and stretching one's limbs. The show stars the silly but lovable Monkey D. Luffy who's power is possibly the most creative and awesome in the show. He's made of rubber and has some great clashes. The show can be seen on Cartoon Network's Toonami and there is also a game out called One Piece: Grand Battle featuring most of the main characters and villains.