NOUN: 1. In Latin, a noun derived from a verb and having all case forms except the nominative. 2. In other languages, a verbal noun analogous to the Latin gerund, such as the English form ending in -ing when used as a noun, as in singing in We admired the choir's singing.
First, let's take a look at the phrase 'look forward to'. 'to' is not an infinitive in this case, rather, it's a preposition.
Second, what follows a preposition? Hm...the answer is noun. "I am looking forward to our meeting." (OK, 'our meeting' is a noun phrase.) "I am looking forward to meeting you." (OK, meet-ING is a gerund used as a noun)