Remote Control Question

[buck12]

SUB and TRI in remote control menu, what do these terms mean?
I found the rest of the them but these two baffle me.
Remote is for a Double Horse 9116

ELEV = Elevator (cyclic movement forward or backward)
AILE = Aileron (cyclic movement side to side, slide left & right)
RUDD = Rudder (to increase or decrease tail rotor thrust, spin the tail left or right)
THRO = Throttle (increase or decrease motor rpm, to raise or lower the helicopter in altitude)
D/R = Dual Rate (increase or decrease servo maximum throw)
EPA = End Point Adjustment (increase or decrease to match the servo arm movements with transmitter control
stick travel)

[buck12]

Nobody ever seen these settings?