A sprite sheet is one big image with several frames of the same sprite on it. For example, you can save this animation:
Like an horizontal sprite sheet:
A vertical one:
Or a matrix:
In the following section you will know how to export and import this kind of images into Aseprite.
To import a sprite sheet use File > Import Sprite Sheet option. Then you can select the file to import the :
A texture atlas is an huge image with all the graphics, sprites and images that a game will use. It's called "texture" because the image can be loaded into the video memory, to render graphics on screen with hardware acceleration.