If the word or phrase following a verb is a noun, a preposition or an adjective and it tells us something about the subject of the sentence, then that sentence's verb is called "intensive":
(a) Max became a doctor. (noun)
=> "a doctor" tells us who Max is.
(b) The cat is in the kitchen. (preposition)
=> "in the kitchen" tells us where the cat is located.
(c) Sam seems happy. (adjective)
=> "happy" describes Sam's state of being.
Note, "intensive" means, to cover a fixed area (similar to agricultural term "intensive farming" i.e., to work the same, fix plot of land), whereas "extensive" means, to cover a wider area.
Intensive verbs are concentrated to one, fixed structure. Words or phrases following an intensive verb function as subject complements; i.e., they complement the subject (they tell us about the subject), they work with the subject, not the verb.
Extensive verbs are not concentrated to a fixed structure. Words or phrases following an extensive verb function as the verb's object; they work with the verb, not the subject.