A human pyramid is, quite simply, a
pyramid made of
humans. Not exactly
built to last. It is generally accomplished by having a large group of
people stand together in a row to form the
base of the
pyramid. Another, smaller group of people then climb up and stand on the backs or shoulders of the group below them. More people pile up, in smaller rows, each
tier supported by the one below it, until ultimately reaching the
pinnacle, where a single person stands atop the group.
Obviously, it's a good idea to have the largest group at the bottom, and the smallest group at the top, not only because this defines the shape as a pyramid, as opposed to a square or other shape, but also because the people at the bottom have to bear all the weight. Though I do believe I recall an inverted human pyramid (only it was made more of sheep than humans] riding a motorcycle in the Wallace and Gromit cartoon A Close Shave... but this must be regarded as an unusual exception.