Definition of "inclusion"

(countable) An addition or annex to a group, set, or total.  examples

(uncountable) The act of including, i.e. adding or annexing, (something) to a group, set, or total.  examples

(countable) Anything foreign that is included in a material,  examples

(countable, mineralogy) Any material that is trapped inside a mineral during its formation, as a defect in a precious stone.  quotations  examples

(cytology) A nuclear or cytoplasmic aggregate of stainable substances.

(histology) An object completely inside a tissue, such as epidermal inclusion cyst, a cyst in the epidermis.

(mathematics) A mapping where the domain is a subset of the image.  examples

(obsolete) Restriction; limitation.