Diacylglycerol lipase is an enzyme that hydrolyzes a fatty acid from a diacylglycerol (glycerol with only two fatty acids esterified to it) to yield a monoacylglycerol and a free fatty acid.
Diacylglycerols arise from action of triacylglycerol lipase on a fat (triacylglycerol), which hydrolyzes one of the three fatty acids from it (at position one or three). Further digestion of the monoacylglycerol requires the action of monoacylglycerol lipase.