Lunch is most commonly "almuerzo" in my experience, with some variation. I think there are some Europeans and perhaps pockets of Latin Americans who use "comida" to refer to either lunch or dinner as a meal, while most people use it to refer to food in general. Dinner is "merienda" in some places, while many others reserve the common "cena" for dinner and use "merienda" to refer to an afternoon snack.