Even though an alto is a woman with a relatively low singing voice, the word 'Alto' actually came to be as a way to describe a man's voice who sings high. You know, back in the day, they were weird about having women sing sometimes, so you would often have boy choirs or all-men choirs where guys took the higher parts. So 'alto', originally describing a man's high voice, is from the Latin root, altus, or 'high'.
As an alto singer, I pride myself on having the best of two worlds when it comes to vocal range. On one hand, I can sing some sweet angelic high notes in my head voice. and on the other, I can give you some strong, thick, powerful belts in my lower range. Think of singers like Ella Fitzgerald and Adele who are simply unmatched when it comes to emotional inflection and rich tone. The alto range is where it's at!
Many will say that the range of an alto is usually from F3 to F5, but I like to think of it closer to F3 to D5, especially when we're talking about belting range in pop or musical theatre styles. If your range is slightly lower, you may want to label yourself as a contralto, which is sometimes even cooler! I'm always jealous of women who can hit low notes around the C3 range in a tone that really resonates (mine is thin). If your range is a bit higher, consider yourself something called a mezzo-soprano.
Keep in mind that all of these terms stem from more classical styles of singing, so there's no need to get too hung up on it if you're not a classical singer.