Snap?
Yup, a snap is the same as a snap roll. To do a snap, the wing must first be stalled. At that point, yaw and roll coupling will produce a stable spinning flightpath. An undesireable snap can occur when a plane enters a stall without warning.
The only requirements for a snap are a high angle of attack and an initial yaw. Speed, flight path, and power setting don't matter. That's why you can do climbing or diving snaps. You can also do them at any speed. Just pull back to get the high angle of attack and introduce a yaw. A spin is just a snap at low speed.
To avoid a snap don't pull the elevator all the way back.
Tom