VerbType: verb type
We already split auxiliary and non-auxiliary verbs at the level of POS tags but some tagsets mark other distinctions.
Aux: auxiliary verb
Verb used to create periphrastic verb forms (tenses, passives etc.) In many languages there will be ambiguity between auxiliary and other usages, thus the same verb should get different tags or feature values depending on context.
Cop: copula verb
Verb used to make nominal predicates from adjectives, nouns or participles. Some languages omit the copula or use other means to create nominal predicates. In languages that have copula, it is often the equivalent of the verbs “to be” or “to become”.
Examples: It is purple. He just became father.
Mod: modal verb
A group of verbs traditionally distinguished in grammars of some languages. They take infinitive of another verb as argument (with or without infinitive-marking conjunction, in languages that have it) and add various modes of possibility, necessity etc. to the meaning of the infinitive. There are other verbs that take infinitives as arguments but they are not considered modal (e.g. phasal verbs such as “to begin to do something”). The set of modal verbs for a language is closed and can be enumerated.
Note that some languages (e.g. Turkish) use special forms of the main verb instead of combining it with a modal verb.
German examples: dürfen (may), können (can), mögen (want/like to), müssen (must), sollen (shall), wollen (want to), wissen (know to)
Czech examples: muset (must), mít (shall, have to), moci (can), smět (may, be allowed to), umět (know to), chtít (want to)
Light: light (support) verb
Light or support verb is used in verbo-nominal constructions where the main part of the meaning is contributed by a noun complement. An English example would be to take a nap, where take is the light verb. It is often the case that the light verb can also function as a normal verb in the language (cf. to take two dollars). If the light verb constructions are used frequently in a language (e.g. Hindi or Japanese) or if there is a dedicated light verb that cannot be used as normal verb, it makes sense to mark light verbs with a dedicated feature value.
Japanese example: suru