What is "Boost"/"Super Boost" in the PW127M/N?
"Boost" is an informal name for the ATR72 "Automatic Takeoff Power Configuration System" (ATPCS) which allows for higher than normal takeoff weights. 

Higher weights are allowed because the system automatically:

1) senses an engine failure

2) feathers the bad engine

3) applies up to 10% increased power to the good engine. 

Theoretically a super sharp pilot could do it all just as well, but the ATPCS does it automatically for an increased level of safety. 

Other aircraft manufactures may call it "Automatic Performance Reserve" (APR)

ATR 72-600 Brochure