When reading articles or tips about taking pictures you're going to come across the words Prime Lens from time to time. Which is good to know that in order for that tip to work you're going to need a prime lens but it doesn't really help if no one tells you what the heck a prime lens is. So hopefully this helps.
A prime lens in simply a lens that doesn't move. Or rather a lens that doesn't zoom.

This 50mm lens is just a 50mm lens. It can not magnify a picture at any other length than 50mm. What does the mm mean at the end of the 50? Well that means that this lens pictured above makes a subject look 50 millimeters closer in front of me than it really is. This focal length is all that this PRIME lens is capable of. So a Prime Lens is a lens that only has one focal length.

The difference is that a zoom lens will give me a range to chose from.

On the right is my 50mm and on the left is 18-135mm. The 50mm is the prime lens because it only has one length it can shoot at. While the 18-135mm can shoot and magnify things anywhere between 18mm and 135mm.

I am NOT a fan of the zoom lens. I understand that people find them to be convenient and in many cases cheaper because it's like getting a bunch of lens in one. But the truth is, I think they suck. If you're shooting in manual mode than you have to be aware of what your focal length is because ALL of your settings change every single time you change your focal length. AND if you're shooting a wide angle shot at 18mm you still have to shoot at higher ISOs, lower speeds, and smaller apertures on a zoom lens that you would on a prime lens because your light still has to travel though this large ass lens. Remember Light is the key to a picture without it you can not have a picture. Light makes everything possible....(which totally sounds like a fortune cookie saying). So to sum up:

A Prime Lens is a Lens that only have one focal length.

A Zoom Lens has a range of different focal lengths.