HTP in stage lighting stand for Highest Takes Precedence.
It is the opposite of LTP.
What this means is a DMX value sent to a channel must be higher than the current value in order for the DMX value of that channel to change.
For example if channel 1 has a value of 128 and a new DMX value of 175 is sent to that channel the the channel will now have a value of 175, because 175 is higher than 128. But if channel 1 has a value of 128 and a new DMX value of 50 was sent to that channel it would not change as 50 is lower than 128 .