Unpolarized Light: is it always linear or could it be elliptical? Unpolarized light is essentially polarized light in every direction i.e. there are so many waves radiating, that each wave oscillates in a different direction. Polarized light can either be linear or elliptical. Is light from the sun or a lamp all linearly polarized or could they/are they elliptical? Is most polarization in nature linear?
 A: It can either be linear, or elliptical... or any other! There are not just 2 possibilities. 
The terms "linear" or "elliptical" refer to the basis that we have chosen. If we choose a linear description, we can be lucky and find a beam which has only one-axis component. That's linear light. However, most beams will have both components, because most light isn't purely "linear".
The same happens if we choose a circular basis. We can be lucky to find a clockwise polarized beam, but that's not very probable actually.
So, going to your final question, most light in nature is randomly polarized. This is often called "incoherent light", and it means that the electric field points in a random direction every single time. There's no way to predict where it will be pointing afterwards.
Since the light from the Sun is like this, this is usually called "natural polarisation". Most lamps also emit this way. You can find some screens where pixels make it linearly polarized, but most of it is random. Notice that most light bulbs are made by fluorescence.
To be precise, the atmosphere adds a small linear component. And there are many lightbubs that emit with a certain polarization. Of course, they will if their glass is a polariser.
