Trash
Trash has 2 meanings
Terrible
Trash is a way to remark on the "terribleness" of something, whether it be an athlete's ability, the taste of a meal, or the appearance of an outfit. For example, if you think a celebrity's outfit is ugly, you might say, "That fit is straight trash!"
As you probably inferred, the slang term comes from the actual meaning of garbage or trash. It represents something unusable that you deem void in value. Because of its harshness, you should probably judiciously use the term not to hurt others' feelings.
For example, if you tell someone they are trash, you say they have no value. This is why most people use the term behind others' backs, especially when they are on social media, where everyone is a critic.
Example
I can't believe Avatar made as much money as it did. That plot was trash
Agreed, but people saw it for the effects, not the story
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A gaming term that refers to the non-boss enemies in a raid dungeon in World of Warcraft; usually found together in groups scattered throughout the dungeon and are much easier to kill than the bosses.