Primary membrane lipids are phospholipids, the main class of lipids making up the cell membrane.
Secondary membrane lipids include sphingolipids, sterols and other classes of lipid. This is due to their non-essential function in the formation of membrane, but instead allow the modulation of membrane properties. For example, sterols (which includes cholesterol) are able to thicken the membrane, allowing the formation of membrane rafts.
[There doesn’t seem to much (if any) on the internet about primary and secondary membrane lipids so I am unsure how important this actually is]