Question

Please, can someone explain to me what simple pendulum means?

Answer 1

A simple pendulum consists of a mass m hanging from a string of length L and fixed at a pivot point P. When displaced to an initial angle and released, the pendulum will swing back and forth with periodic motion.

Answer 2

its an idealised mathematical model.

yes, it is a pendulum, ie a mass suspended on a string or whatever that swings back and forth.

https://en.wikipedia.org/wiki/Pendulum

but a number of assumptions allow us to model it mathematically, including some of these:

Answer 3

ouch, drawing failed

assumptions include

point mass [so, eg, no rotation]
small displacement, so linear
massless string
total conservation of energy......