Linking verb

A linking verb is a verb that joins the subject of a sentence to the complement (the word or phrase needed to finish an idea).
Here are some examples of linking verbs:
('is' and 'are' are the linking verbs that connect the subject to the adjective or adjective phrase that describes it.) 
Many languages have one main linking verb. In English, this is the verb "to be". People use this verb to show how or what something or someone is. Some languages, for example Portuguese and Spanish, have two different verbs for the two meanings of this verb.
Other languages, for example Arabic and Russian, do not have any linking verbs. That is because most languages without linking verbs have inflections, or word endings, that show what part of the sentence words are. Speakers of those languages can join the subject to the complement without any extra words since they share the same kind of inflection. For example, to say "I am a cat" word by word in Russian, a person only says "I cat" (Я кошка in Russian), but it is obvious to the Russian speaker what the meaning is because both words are in the nominative case, or the word form that shows that a word is the subject of a phrase. Since both words are in the subject form, the words are both linked together.