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.

Related

NEXRAD The US network of 150-odd weather radars. Each has a four-letter ID like KTLX.
Tilt One sweep of the radar at one elevation angle. A volume is a stack of them.

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