It may be a "directly artistic act of expression that anyone can do", or it may be an "expressive act that requires special technical ability", or it may be an "expressive act that is based on interpretation". Performance is also something that has not been clearly studied. It is probably the least researched area in the field of art.
However, in some cultures, performance holds the highest cultural significance, that called "ceremoniality" or "Rituality". (The theatre play is the piece, not a performance, but rather it is in which art field in relation to the film.)
After the war, in contemporary art in the Western, there was a cultural evolution called "performative" from a sociological perspective, that related to the language evolution. -> Roland Barthles