Many a tourist has shown up at a restaurant at noon for lunch and had to wait an inordinate amount of time for service. Many restaurants that cater to tourists will have service throughout the day, but others that are geared towards locals may only serve during typical mealtimes, and noon is not one of them!
Here's a list of the names of meals and times that they're generally consumed.
1. Desayuno

© 2006 Suzanne BarbezatA light breakfast eaten first thing in the morning - perhaps just coffee, hot chocolate or atole (a thick hot drink that is made with corn, rice or oats) and sweet bread or fruit. A heavier morning meal is usually refered to as almuerzo.
2. Almuerzo

© 2006 Suzanne BarbezatThis is a heavy breakfast or brunch, usually eaten sometime between 9 am and noon. This morning meal may consist of an egg or meat dish, or a dish made with fried tortillas and a spicy
sauce such as chilaquiles or enchiladas.
3. Comida

David Buffington / Getty ImagesGenerally eaten between 2 and 4 pm,
comida is the main meal of the day. It may consist of several courses, including soup (
sopa) or salad (
ensalada), a main dish (
guisado) and dessert (
postre). It is often accompanied by a fruit flavored water (
agua fresca).
Many restaurants offer comida corrida, a set meal with a few options. This is often the most economical choice though prices can vary from around 30 to 100 pesos. Many businesses and offices close between 2 and 4pm, not for "siesta" as is often thought, but for comida, so that workers can go home to enjoy the main meal of the day with their families. Correspondingly, traffic tends to be heavy between 1:30 and 2:30 pm on weekdays.
4. Cena
For many Mexicans the final meal of the day may consist of just a hot drink and some bread, but it could also be a nice meal consumed in a restaurant, or a chance to try out some authentic Mexican tacos at a street stand.
5. Botanas, antojitos and tentempiés

PhotoLink / Getty ImagesThese are different terms that are used to refer to snacks and you'll find plenty to snack on as you go about your day in Mexico. Botanas generally accompany drinks and can be as simple as salted peanuts or nachos and salsa. An antojo is a craving and antojitos satisfy those cravings for yummy Mexican snacks - these tend to vary throughout the country.