Cytoplasm is the gel-like substance that fills the cells. It contains all the organelles [specialized structures inside the cell] and is important for many cellular processes such as metabolism [the chemical reactions that keep the cell functioning].
For example, imagine a cell as a room. The cytoplasm is like the air filling the room. It contains furniture [organelles] like the mitochondria [produces energy] and ribosomes [makes proteins] that are essential for the cell’s function.
Very Simple Definition:
Cytoplasm is a jelly-like substance that fills a cell. It helps keep the cell healthy and working properly.
You can think of the cytoplasm as the air filling the inside of a balloon. Just like the air keeps the balloon’s shape, the cytoplasm keeps the cell’s shape and helps it do its job.