Meta-gaming is having your character know information only revealed to you ooc'ly. Since your character can't logically just know something that was mentioned to you and not them, it is advised you don't do it. It also makes no ic sense for your character to know something that way.

Having a character that has telepathy to know other's secrets is not advised. It can become annoyingly deus ex machina, and you can only know what is revealed to you by the player. It wouldn't make sense for your character to know their deepest darkest secrets and not how cold they like their milk, for instance.

For example, we have a player named Bob and some players meta-gaming.

 [Bob]: says: Greetings, sir.
 [Thalen]: says: Hello Bob!
 Bob blinks.
 [Bob]: says: ...Have we met before?
 [Killhaxx]: says: can i join ur guild?
   [Bob]: says: ...
 [Bob]: says: (Mutters) Who told you about the band of Defias -
 [Guardlol]: says: You're under arrest for working for the defias!
 [Bob]: says: What?  No...You have no proof!
 Bob grips his sword defensively, glaring at the human soldier.
 [Guardlol]: says: It says it in your guild name.
 [Bob]: says: ...
 [Guardlol]: says: The one floating above your head stupid.
 Guardlol laughs at Bob.
 [Guardlol]: lol