Agreement or concord (abbreviated agr) happens when a word changes form depending on the other words to which it relates. It is an instance of inflection, and usually involves making the value of some grammatical category (such as gender or person) "agree" between varied words or parts of the sentence.
For example, in Standard English, one may say I am or he is, but not "I is" or "he am". This is because the grammar of the language requires that the verb and its subject agree in person. The pronouns I and he are first and third person respectively, as are the verb forms am and is. The verb form must be selected so that it has the same person as the subject in contrast to notional agreement, which is based on meaning.
