, from the Ancient Greek chole-
(bile) and stereos
(solid) followed by the chemical suffix -ol
for an alcohol, is an organic molecule. It is a sterol (or modified steroid), a lipid molecule and is biosynthesized by all animal cells because it is an essential structural component of all animal (not plant or bacterial) cell membranes
that is required to maintain both membrane structural integrity and fluidity. Cholesterol enables animal cells to not need a cell wall (like plants and bacteria) to protect membrane integrity and cell viability, thus are able to change shape and move about (unlike bacteria and plant cells which are restricted by their cell walls).