The definition of the word "inclusion" as stated by the Oxford Advanced Learner's Dictionary is "the action or state of including or of being included within a group or structure." The secondary definition is "a person or thing that is included within a larger group or structure."
A scientific definition of this word is also available through the Oxford dictionary. The word "inclusion" is listed as a noun. The origin of the word comes from the early 17th century and the Latin word that means "shut in." OxfordDictionary.com offers multiple example sentences, rhyming words and a link for English synonyms and British/World definitions.