[Grammar] correct preposition

[pradeepsaxena]

In continuation to my previous queries, I would like to know what is the difference between
I met her in conference. and I met her at conference

 

[5jj]

I met her at the conference.

 

[emsr2d2]

Or "I met her at a conference".

If you attend a conference somewhere, you are at a conference.
If you are talking to someone or in a group meeting, you are in conference.

There is a situation where an article might not be needed. Sometimes, when a group has an annual conference, they simply refer to it as Conference.

Where is Andy this week.
Oh, he's at Conference.

That would probably be a shortened version of the full name of the conference ie "The Hospitality General Workers' Union Conference", but if both speakers already know the details, they might just say that someone is "at Conference".