Question

what exactly is a split infinitive?

Answer 1

It is when an adverb splits an infinitive in half.

For example:

~ Infinitives: Basically, a verb with "to" in front of it.
To go.
To run.
To walk.

~ Adverbs:
Words that modifies a verb.

~ Split infinitives:
To boldly go.
To quickly run.
To slowly walk.