The most common and most likely answer to this crossword clue is the 7 letter word WEBCHAT
I've seen this crossword clue in The Guardian
W
E
B
C
H
A
T
Buddy explains!
The straight part
We know that "Online discussion" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case online discussion = webchat.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does WEBCHAT mean?
WEBCHAT noun- A conversation that takes place, usually in text, over the World Wide Web.
- To take part in such a conversation.