When it comes to glitter, glequins and sequins, they fall into each category depending on their size.
Sequins (see an example here) are large pieces with a small hole in the center, mostly used for crafts and in fashion. They are, in my opinion, way too big to be used in nail art.
Glitter, on the other hand, is just that: teeny pieces, usually in a dust or powder form, that would be impossible to apply individually.
Which brings us to glequins. Glequin is just a made-up word that we in the nail world use to combine the two previous. Glequins are roughly 1-2mm in diameter and come in different shapes from hexes, to squares and diamonds, to circles, and even hearts, stars, and music notes, etc. They typically come in a little pot or jar and are individually adhered to the nail with clear polish. See examples of glequins here and here and here.
Want to see some glitter placement manis I have done just playing around with glequins (which I prefer to call "glitters" or "loose glitters")?
I used a couple of Pure ICE polishes for this first look:
The rest of these designs were done with some loose hex glitters, or glequins, from Born Pretty Store. The first one is the mani I wore when I reviewed their glequins, which you can read here. And the second was a fish scale looked I created using them. You can see that full blog post here.
The final two designs I'll show you were just the results of playing around with the BPS glitters.
The first is on a base of Distant Memory from Spoiled by Wet'n'Wild, and the last is over Revlon Cupid.
If you were confused about glequins like I was at first, hopefully this helps you clear things up a little!