The infinitive is a non-finite verb form. In Spanish the infinitive can function as a noun and as the complement of many verbs. The infinitive is regards as the "name" of the verb and is the only form of the verb that has an independent entry in most dictionaries.
All infinitives have one of three endings: -ar, -er or -ir. Each ending corresponds to a one of the three sets of endings for regular verb conjugations.