A split infinitive is an infitive with another word, usually an adverb, inserted. Thus 'to boldy go' is a split infinitive from the verb 'to go'.
There is a myth circulating among uninformed English teachers that the split infinitive is somehow incorrect, yet if you ask them they cannot come up with a reason besides "it's wrong". The truth of the matter is that infinitives have been split for nearly seven hundred years, and condemnation of this construction arose in the 1800s by applying Latin to English grammar -- a practice which in the age of modern linguistics is laughable. Language does not conform to arbitrary rules, much less rules from another language.
The next time your English teacher tells you the split infinitive is wrong, ask them why. I promise you will find the non-response hilarious.
The first major sound change law discovered. It described the shift of stops which occured during the change from Proto-Indo-European to Proto-Germanic. It was first postulated by Friedrich von Schegel in 1806, then by Rasmus Christian Rask in 1818, and finally enunciated in its most famous form by Jakob Grimm in 1822. It is composed of three parts:
1. The shift of voiceless stops to voiceless fricatives, thus p > f, t > th, and k > x.
2. The shift of voiced stops to voiceless stops, thus b > p, d > t, and g > k.
3. The deaspiration of the aspirated stops, thus bh > b, dh > d, and gh > g.
Some exceptions to Grimm's Law exist, most notably those stated by Karl Verner in Verner's law.
Thus through Grimm's Law, PIE petro > PG fethra, PIE wodr > PG watr, ghordho > gard, etc.