Laminating is a process where a liquid or transparent, plastic film's applied over a printed sticker or label.
Laminators come in all shapes and sizes. A traditional, wide-format roll-to-roll laminator looks like this:
The printed roll of media (also known as vinyl, or paper) gets put through the rollers. A transparent plastic layer is stuck to it to give extra protection. Here's a close up of how it looks:
You can see the clear laminate coming from the top and the printed media coming from the bottom. Both materials are fed between the rollers, to apply the clear over-laminate.
Liquid lamination is very similar, but instead of a plastic layer being applied, a scratch-resistant liquid is coated onto the printed media's surface. This provides less protection than plastic but is better than nothing, so suitable for labels that require a moderate scuff resistance. It's also very low cost & environmentally friendly because it doesn't use plastic.