In art, performance art is a performance presented to an audience, traditionally interdisciplinary. Performance may be either scripted or unscripted, random or carefully orchestrated; spontaneous or otherwise carefully planned with or without audience participation. The performance can be live or via media; the performer can be present or absent. It can be any situation that involves four basic elements: time, space, the performer’s body, or presence in a medium, and a relationship between performer and audience. Performance art can happen anywhere, in any venue or setting and for any length of time. The actions of an individual or a group at a particular place and in a particular time constitute the work.
Sniggle.net Interesting website with various definitions and examples of performance art.