From Second Life Wiki
Chim refers to the ability of some dance HUDs to animate other avatars in addition to the wearer. It can be used as a noun to refer to a HUD that can do this, or to a wearable accessory prim that allows avatars to request this by touching it. It is also frequently used as a verb to refer to being animated this way. Most chims can animate a limited number of avatars at a time. Examples of typical uses of the word as a noun would be "My chim is full" and "My chim is on my butt". The usual example of the verb form is "Chim me."
The word chim is derived from Chimera, which was a popular brand of dance attachment. It is used in the Second Life sense to refer to dance HUDs which feature chimming, but has been eclipsed by the more encompassing chim.