Tomate vs. jitomate
The Spanish words tomate and jitomate both mean tomato, but their usage varies significantly based on geographic region. The choice between them primarily depends on whether you are in Mexico or another Spanish-speaking country.
Tomate
A1In most of the Spanish-speaking world, including Spain and the majority of Latin America, tomate is the standard and universal word for a red tomato. In parts of Mexico, however, tomate refers to the small, green husk tomato (tomatillo) used in salsa verde.
La paella a veces se decora con rodajas de tomate.
(Paella is sometimes decorated with slices of tomato.)
Compré un kilo de tomate para la ensalada.
(I bought a kilo of tomato for the salad.)
En Argentina le ponemos tomate a casi todos los sándwiches.
(In Argentina, we put tomato on almost all sandwiches.)
Para hacer la salsa verde mexicana, necesitas un buen tomate.
(To make Mexican green salsa, you need a good green husk tomato.)
Jitomate
B1The word jitomate is used almost exclusively in Mexico, especially in the central and southern regions, to refer specifically to the common red tomato.
La sopa de tortilla lleva jitomate, aguacate y chile pasilla.
(Tortilla soup has red tomato, avocado, and pasilla chili.)
Pica finamente un jitomate para el pico de gallo.
(Finely dice a red tomato for the pico de gallo.)
¿Cuánto cuesta el kilo de jitomate en el mercado?
(How much does a kilo of red tomato cost at the market?)
Para los huevos rancheros, se hace una salsa con jitomate asado.
(For huevos rancheros, a sauce is made with roasted red tomato.)
Summary
In essence, the main difference is geographical. Use tomate for the red tomato everywhere in the Spanish-speaking world except Mexico. In Mexico, use jitomate for the red tomato and tomate (or tomate verde) for the green husk tomato (tomatillo). If you are ever unsure, using tomate for the red tomato will be understood almost everywhere, though it might cause slight confusion in parts of Mexico.