Infinitive, zero infinitive, null infinitive, bare infinitive

An infinitive is made up of the word to and the verb:

To go, to walk, to see, to crawl, to suffer.

If we remove the word to, we obtain what is variously known as a "zero", "null" or  "bare" infinitive.

go, walk, see,  crawl, suffer.

Don't let the fancy terms scare you. They had to call it something.