Sterol lipids, such as cholesterol and its derivatives are an important component of membrane lipids, along with the glycerophospholipids and sphingomyelins.
The steroids, which also contain the same fused four-ring core structure, have different biological roles as hormones and signaling molecules.
The C18 steroids include the estrogen family whereas the C19 steroids comprise the androgens such as testosterone and androsterone. The C21 subclass includes the progestogens as well as the glucocorticoids and mineralocorticoids.
The secosteroids, comprising various forms of vitamin D, are characterized by cleavage of the B ring of the core structure. Other examples of sterols are the bile acids and their conjugates, which in mammals are oxidized derivatives of cholesterol and are synthesized in the liver.
References
Wachtler V, Balasubramanian MK. Yeast lipid rafts? - An emerging view. Trends Cell Biol. 2006 Jan;16(1):1-4. PMID: 16337381