What does "mast cell degranulation" mean in an allergic reaction?

Mast cell. Definition protein involved in mast cell degranulation. Mast cell is a large, ovoid cell of hematopoietic lineage, with a centrally located nucleus and numerous large, intensely basophilic granules. The binding of an antigen to its specific immunoglobulin-e antibody on the mast cell surface triggers the release of the mc granules. Mast cells are involved in hypersensitivity reactions.