Cytoplasm is the gelatinous liquid that fills the inside of a cell. It is composed of water, salts, and various organic molecules. Some intracellular organelles, such the nucleus and mitochondria, are enclosed by membranes that separate them from the cytoplasm.
Cytoplasm's a funny term. So what does "cyto" mean? "Cyto" means "cell", "plasm" means "stuff", so it's "cell stuff". So think about a cell as a big water balloon, and the water balloon has little pieces of fruit floating around in it. And the cytoplasm is the water in the water balloon, and it's a little bit thicker than water, but it makes up the majority of the inside of most cells. Now, inside the cell, inside that water balloon, there's a nucleus and there's other so-called organelles, like mitochondria, or lysosomes, or the endoplasmic reticulum and other unpronounceable organelles, but the cytoplasm is the ocean in which all of these organelles float.