Exocrine glands contain a glandular portion and a duct portion, the structures of which can be used to classify the gland.
The duct portion may be branched (called compound) or unbranched (called simple).
The glandular portion may be tubular, acinar, or may be a mix of the two (called tubuloacinar). If the glandular portion branches, then the gland is called a branched gland.
Therefore, a compound gland has a ductal system that is branched and a simple gland has a non-branched ductal system.
This is also helpful in differentiating the secratory portions of the glands...