Rebanada vs. rodaja

The Spanish language has a variety of words to define different types and shapes of slices. Two such words are 'rebanada' and 'rodaja'. Although they are often used interchangeably, they have subtle differences corresponding to shape, context and items they are usually associated with.

Rebanada

'Rebanada' signifies a flat, often rectangular slice which is usually cut from a loaf of bread. However, it can also refer to thin pieces from other large, oblong items.
Quiero una rebanada de pan tostado para el desayuno.
(I want a slice of toasted bread for breakfast.)
Podrías cortar una rebanada de ese pastel?
(Could you cut a slice of that cake?)
Una rebanada de queso hace la hamburguesa más deliciosa.
(A slice of cheese makes the burger more delicious.)

Rodaja

'Rodaja', on the other hand, refers to disk-shaped or round slices, typically cut from cylindrical objects like fruits (e.g., oranges), vegetables (e.g., cucumbers), or sausage.
Me gustan las rodajas de naranja en mi agua.
(I like orange slices in my water.)
Corté algunas rodajas de pepino para la ensalada.
(I cut some cucumber slices for the salad.)
Vamos a necesitar una rodaja de chorizo para la paella.
(We're going to need a slice of chorizo for the paella.)

Summary

'Rebanada' and 'rodaja' both refer to a 'slice', but these Spanish words have specific context of use based on shape and type of items. While 'rebanada' refers broadly to flat slices generally from oblong items like bread or cake, 'rodaja' denotes round and typically smaller slices mostly from cylindrical objects like fruits, vegetables or sausages.