"Trending" is a mutilation of the
English language that means "currently popular." It derives from a sad misunderstanding of the verb "to trend" as meaning "to become a
trend."
Twitter's "
Trending Topics" list has probably contributed to this degeneration.
A: I said "
Wikileaks is trending now" when I should have just said it was a popular news story. What's happening to me?!
B: The
internet has ruined your mind. Reading
pop culture on the internet is the worst thing you could do to your ability to
communicate in plain English short of taking up a career in contract
law. Hence "trending."