To talk in away which offends the opponent in dialogue. Commonly used on the basketball court or when teaching your chinese exchange student how to speak english.
Chad A: Hey Xiyan do you want to learn how to talk trash?
Xiyan: What?
Chad A: Shut up fatass, imma bust a nut if you get cocky on me!
Xiyan: What?!
In the course of a competitive situation putting down your opponent verbally or saying how good you think you are. Oftenly involving talk of moms or sisters.
Examples of Trash Talk
"You couldn't tackle me in a phone booth"
"You better stay out of the paint or I'll block you so hard I'll make your momma hurt more than I made your sister hurt last night"
"I'm so fast you couldn't see me with a telescope"