Basically Thrash is a fast paced Metal style that usually includes lots of Palm Muting on the top E string and mega fast solo's.
"Yeah, they were Thrashy as fuck!"
* Death Angel
Thrash metal songs typically use fast, percussive and low-register guitar riffs, overlaid with shredding-style lead work.
Possibly the four biggest bands in the Thrash Metal genre include: Slayer, Megadeth, Metallica, and Anthrax.
Thrash guitar solos are almost exclusively played at high speed, as they are usually characterized by shredding, and use techniques such as sweep picking, legato phrasing, alternate picking, string skipping, and two-hand tapping. Thrash lead guitarists are rooted in the New Wave of British Heavy Metal movement.
The speed and pacing of the songs is what defines thrash metal. The music tends to have a visceral, propellant feel to it due to its drumming style, most commonly utilizing the snare drum on the 1/2 beat, or the 2nd and 4th beats of the measure. Frantic bass drum use is also common. Thrash drummers often use two bass drums. Some thrash drummers are revered as some of the "best drummers in rock music".
Consisting of pure angst of the teenage soul, high speeds and killer guitar solos. It will be a blast to your face.
Metallica - Creeping Death
...and many many others, from the 80 thrash metal invasion.
Thrash metal's origins trace back to the early 1980's, and San Fransisco is considered the birthplace of most of the thrash greats. Thrash metal bands include Metallica, Megadeth, Slayer, Anthrax, Testament, Exodus, Kreator, etc. It has proved to be very influential to almost every metal style that has come about since it's inception, and has experienced somewhat of a popularity revival in recent years.
Dude 2: Uh, I'm going to go see Megadeth in 2 weeks..
Dude 1: ...You bastard!