Apocrine is a term used to classify exocrine glands in the study of histology. Cells which are classified as apocrine bud their secretions off through the plasma membrane producing membrane-bound vesicles in the lumen. This method is also called decapitation secretion. The apical portion of the secretory cell of the gland pinches off and enters the lumen.
Apocrine secretion is less damaging to the gland than holocrine secretion (which destroys a cell) but more damaging than merocrine secretion (exocytosis).
An example of true apocrine glands are mammary glands, responsible for secreting breast milk.