Where is the ester bonds in lipids?

The ester bonds in lipids are found where the fatty acids of the lipid join to the glycerol back bone of the lipid.

Lipids are made from two kind of molecules namely Glycerol and Fatty acids.  A glycerol molecule is made up of three carbon atoms with an alcohol group attached to each of the carbon atoms  and hydrogen atoms occupying the remaining positions.

A fatty acids consist of an acid group at the end of the molecule and a hydrocarbon chain.

In a process called esterification, the acid group of the fatty acid joins to the alcohol group of the glycerol molecule and water is released resulting in the formation of a linkage called an ester bond.