Tilt

One sweep of the radar at one elevation angle. A volume is a stack of them.

Related

VCP The scanning pattern the radar is running. Storm modes sweep faster and use more tilts than clear-air modes.
Level 2 / Level 3 Level 2 is the raw volume, every gate of every sweep. Level 3 is the smaller set of processed products the NWS publishes from it.

See it on real storms: open the radar, or read reading the radar.