Spirit of Wolf is more commonly known by its acronym SoW.
The casting of this spell is limited to members of the Beastlord, Druid, Ranger and Shaman character classes. Beastlords are able to cast SoW at level 24, Druids at level 10, Rangers at level 28 and Shamans at level 9. Players of every class can have this spell cast upon them at any level.
The purpose of this spell is primarily to accelerate the rate of movement at which a character can walk or run (Increases Movement by 34% (Level 9) to 55% (Level 50)). This is especially important when trying to escape high level mobs that a player is having trouble killing, and also aids in speeding up run time from zone to zone.
It is common to see Druids and Shamans offering to cast SoW to other players for a small donation of platinum (the in-game EverQuest currency) in a central location such as the Plane of Knowledge. For several years this was the most sought after buff in the game.
Other buffs (beneficial spells) that increase movement rate include "Spirit of Eagle" (Increases Movement by 57% (Level 54) to 60% (Level 60) plus Levitation, See Invisible, and Infravision) and various Bard songs.