"Peaks" is an optional feature of the EGPWS. It's main purpose is to provide greater situation awareness of terrain features when at cruise altitudes in case of unplanned desents. Without the peaks feature activated, terrain is only displayed within 2000' of the aircraft altitude.
Honeywell has an excellent website dedicated to EGPWS, www.egpws.com, where you can even download a Pilot Guide, amongst over goodies.