What is a telephoto? and what is a telephoto lens?

What is a telephoto? 
A telephoto is one taken with a telephoto lens.

What is a telephoto lens?

It is not a complete coincidence  that telephoto and telescope sound a bit alike. Both serve in magnifying things. In fact, with a big enough telephoto lens, you can kind of use it like a telescope and have a play with astrophotography.

A telephoto lens is an expensive, long lens you can buy to fit over an SLR or DSLR and it's purpose is to achieve great magnification of things that are really far away. It has an optimal effect where it flattens a scene so that the picture appears as though it's nearby when in fact you may be miles away. You can also get super-telephoto lenses which have even greater magnification. This makes them useful for wildlife photography, photographing things like planes or nature shots of landscapes in the distance, and it's also useful for stalkers.. :D

Some signature marks of a telephoto include beautiful bokeh, and also the fact that it's notoriously prone to get blurry shots unless you keep the camera perfectly still. Even pressing the shutter to take the photo can vibrate the camera so that the whole picture comes out blurry.