To freeze something or someone
When the Ghostbusters found themselves chased by the giant Mountain Spirit of Haunted Mountain, Jake Kong Jr. asked Tracy to pull something out of his Ghostpack that they might use against the Spirit, and Tracy produced the Freeze-O-Matic. Jake immediately used the device to turn the Spirit into solid ice. According to Eddie Spenser Jr., it would take the monster a week to defrost.
The Freeze-O-Matic was first used in the episode Train To Doom-De-Doom-Doom.