A copula is type of verb or affix that is an obligatory element in a predicative sentence in the case of nonverbal (nominal, adverbial) predicates. In its base form, the copula has no meaning other than its predicative function; if it is an independent word, it is generally the same as the substantive verb ‘be.’  The base form is found to appear in sentences that fulfill the following four criteria: a) stative-like,[1] b) declarative mood, c) present tense and/or the least marked (most neutral) aspect, and d) appear in third-person singular. Copula type is determined by the relationship of the copula to the lexical verb. (Lexical verbs express meaning other than, or in addition to, copulative function.)

Types:

NoCop:  The language does not have a copula.

Cop=VInfl: The copula, when explicit, is inflected just as lexical verbs.

CopNoVInfl: The copula, when explicit, is not inflected, unlike lexical verbs.

Cop=VNotInfl: Neither the copula nor lexical verbs are inflected.

CopNoV: The copula is an independent word but not a verb.

Cop=Aff: The copula is an affix.[2]

When a language displays more than one type, two values can be listed. If one type is structurally dominant, a slash (/) can separate the two values, with the dominant value appearing first; if neither is dominant, the two are listed with an ampersand (&) separating the two.

[1] This means that only the predicate is expressed in present tense or as a general statement.

[2] Predication of nonverbal lexical elements by verbal affixation should be listed here, such as predicative nouns and adjectives displaying verbal inflection. These constructions should be detailed in the commentary.