Literally 'one bowl of rice', but can refer to a simple meal or a single serving of food. Often used in set phrases or literary contexts.
I won't forget the kindness of even a single meal.
He worked without even taking time for a quick meal.
a night's lodging and a meal
Compound of 一 (one) and 飯 (meal/rice). The exact historical derivation is uncertain, but it follows a common pattern for counting servings.