A split infinitive is an infinitive that

a. is used without the word "to."

b. has a word between "to" and the verb.

c. must have a subject.

d. is used as an adjective or a noun.

A split infintive is an infintive that b. has a word between "to" and the verb. (Why do you think they call it split?)

Examples:

to boldly go where no man has ever gone before

she seems to really like it

P. S. Learn to Google