What is the difference between textures and decals

From what I understand, textures are based image of meshes while decal is what apply to it later during runtime.

Do I understand it correctly?

The texture object is very similar to the Decal object. However, a Decal is projected on a surface like with a projector on a wall. So it can go around Corners and on top of any other things, like on top of a texture. Think of a wall with stickers, the wall could be made of a texture, the stickers are decals on top of the wall.
For a texture you also need UVs in place, a Decal is just projected on top of it without any UVs needed

thank you!