Let me try to explain it:
Lets say you want to SL at 60. Inorder to achieve this, you must put the SELL ORDER in the system. The trigger price is the price at which the order is issued to the system.
Example trade:
You purchase ABC shares at 70 with a TGT 100 and SL 60 and SL trigger 65
After some time, the share price starts falling.
As soon as the share price reaches 65(trigger), an order to SELL the shares at 60 would be placed.
Thus,
Trigger price = price at which the order to SELL at SL must be placed!