An example of a split infinitive is: "to boldly go." In this phrase, "boldly" splits the infinitive "to go."

"To stem" is an infinitive. When an adverb is placed between "to" and "stem", it creates a split infinitive. A split infinitive is not a part of speech but a highly controversial grammar issue. Star Trek's "to boldly go. . ." is, perhaps, the most famous split infinitive.

An http://www.answers.com/topic/infinitive is the "to" form of a http://www.answers.com/topic/verb, as in "to play." A split infinitive is a http://www.answers.com/topic/phrase in which to is separated from the verb. The sentence "I decided to quickly and directly go home" contains a split infinitive. Some people consider it poor style, or even incorrect style, to split an infinitive. I prefer to think of split infinitives as generally unnecessary. Given a little thought, one can usually construct a better sentence. The sentence "I decided to go quickly and directly home", is more easily understood.

A split infinitive is when the base form of a verb is combined with 'to': to dance, to walk etc, then if you place in an adverb between the two words, you end up with a split infinite. I.e. 'To boldly go where no man has gone before'.