The INFINITIVE form of a verb is the form which follows to:
This form is indistinguishable from the base form. Indeed, many people cite this form when they identify a verb, as in “This is the verb to be“, although to is not part of the verb.
Infinitives with to are referred to specifically as TO-INFINITIVES, in order to distinguish them from BARE INFINITIVES, in which to is absent:
|Help me to open the gate||Help me open the gate|