One is the number of God, The One, the Creator. One is considered the "original number"; it is the "unit" off which we base everything else.

According to numerology, people can be classified based on their number. This "number" is derived using gematria, usually, although other tricks are also utilized. Figure out your number however you like, I guess.

"One people" in numerology are supposed to be dominants, leaders. They are tough people that don't shake easily and stick to their goals. (This is because if you divide or multiply by 1, the result is the original number, unchanged.) Sometimes "one people" are also assumed to be stiff and stern, probably because of the upright stance of the number itself.

One is the number of the point; the unity. It signifies the point in geometry because, well, duh; the point is one-dimensional. One is the creator, but it is also powerless to become anything new without help. There's a reason this is a male number, the number of the Father: it is the creative power, but it is of course sterile without the female two.

Interesting fact: In Ancient Greece, one was not considered a number. "A number" was any grouping of things; and one was not a group, it was just the thing. But you think that's bad; in those days, Zero didn't even exist.