What is baking?

So i’m a beginner with unreal and i started to see “baking” really often but it seems like there are two types. Lighting and 3D modelling. Can anyone please explain what they mean.

light baking is when you do all the work to render the lighting and encode it into the art asset textures so the users pc does not have to. its cheap and high quality. but its also static. baking textures in a 3d program is kind of the same. you can take a very high poly with lots of details and bake the normal directions onto a texture, and apply that to a much lower poly version. ue4 will then use the normal map to calculate lighting as if it were the high poly asset.
you can also bake AO to get much higher quality AO than the engine can do in real time.
its all about precomputing the hard stuff so that the user does not have to. you could ship a game with 20 million polygon space ships (cough star citizen cough) but then no one could run it.

It’s basically a way of applying a set of textures to a 3D model so that they don’t have to be calculated anymore, the result is something that can no longer be modified without rebaking the textures.