Original: Sebaceous glands secrete the oily, waxy substance called sebum (Latin, meaning fat or tallow) that is made of fat (lipids), wax, and the debris of dead fat-producing cells.
Simplified: Sebaceous glands produce the oily, waxy substance called sebum (Latin, meaning fat or tallow) that is made of fat (lipids), wax, and the leftover dead fat-producing cells.