____ were introduced by Allan Kaprow in the late 1950s and 60s.These were scripted events that took place over a predetermined period of time with...

I believe that what you are referring to are events known
as "Happenings." Kaprow organized over two hundred "happenings," which were considered
an art form, considered "performance art." Considered either a performance, an event or
situation. While these things were planned, sometimes performers would also improvise.
They could take place in the lofts of studio apartments or in alleys. Because these were
performed for audiences and there were not strict separations between the art
performance and the members of the audience, at times, the audience became a part of
this form of art.

"Happenings" were first developed in the
1950s and '60s; the term "happening" later came to describe any "gathering of interest,
which could be a gathering of people at a pool or billiard hall or musicians at a jam
session. It could even refer to a "fancy formal party."