Chances are if you've ever looked up at a cloudless blue sky, you've seen little spots floating around in your vision. Since the general public usually comes up with better names for scientific phenomena than scientists, these floating spots are known as "floaters" to most people and as "vitreous syneresis" to scientists. Another example of a good, descriptive name vs. an obscure, scientific name is a "housefly," which biology majors spend years learning to call "drosophila melanogaster." It can sometimes take years for a scientist to unlearn the useless name of objects, and lead to frustrating situations. "Harriet, bring me the drosophila swatter! No, no! This is the orthoptera spray! Gahhh!"
Back to the floating spots in your vision, which can come in all shapes and sizes. The are tangled up pieces of protein and gel inside the eye. The whole eye holds about 5 milliliters of fluid, and over 4 of those milliliters are a gel that you're born with called "vitreous humor." As a kid, the vitreous is the consistency of jello. As 100-year-old, that same vitreous is the consistency of water. Between those two ages, the vitreous is liquifying unevenly and forming little water pockets. What happens to those big (on microscopic terms) strands of proteins and other molecules where the water pocket forms? They bundle up into little tangles that then get stuck in the surrounding gel. And there they sit, suspended like pineapple chunks in jello. Only they annoy people even more than pineapple chunks in jello.
The wiggling and dancing that floaters do at the edge of the vision is a result of the natural, darting movements of the eye, called "saccades." Those saccades are usually used to find objects in our peripheral vision and lock onto them. But it's impossible to do that when the speck you're trying to see is inside the eye because it moves when your eye moves! Even if you slow your eye down and try to "follow" the floater, it will slowly move along with your eye, just outside your central vision. It's no wonder they annoy people. It'd be like trying to locate the pebble in your shoe, and after shifting your socks and readjusting your shoe, realizing it is inside your foot. Everybody gets floaters, because everyone gets liquified eye gel called vitreous syneresis. I used to think that knowing what causes them would make them less irritating to people, but I've found out over time that isn't true. Which makes sense when I think about it, since in light of the previous metaphor, it's equivalent to me saying, "Ha! Good news! I know exactly what the problem is, you've got a pebble inside your foot! But don't worry, it's natural."
One last point: if the tiny specks you are seeing when you look at a blue sky are moving with a purpose and not related to your eye movement (almost like ants marching by), that entopic phenomena is caused by white blood cells squeezing one by one through the capillaries on your retina. Neat, right? Eyes are neat.