A trade exception, or traded player exception, is a credit a team receives when it trades away more salary than it takes back, which it can use within a year to absorb a player's salary in a later trade without sending anything out.
HoopSim has no trade exceptions. Salary matching is settled inside each trade: if you are over the cap, you cannot take in salary without sending some back in the same deal, and sending out more than you take back creates no credit for later. HoopSim also has no cash in trades. A team under the cap can absorb salary up to its cap room, which is the only way to take a player back for nothing but a pick.
Rulebook: Salary matching. Related: salary matching, sign-and-trade, cap space.