Call

In the broadest sense, "calling" refers to using the team chat to indicate information about your character to the other members of your party. This is easily achieved by holding down the control key while clicking on an area of the GUI. For example, control-clicking on an enemy (in addition to causing you to attack it) will generate a text message in the team chat that says "I am attacking [enemyname]!" This particular example is also an example of a "target call".

Stategically speaking, having a party of 6 (or more) players spamming the team chat with what their character is doing is extremely confusing, especially in the heat of battle. Therefore, organized parties will generally designate one player as having "the call", who is responsible for identifying which target the party should focus their attention on.