Saturation when it comes to fats refers to how fully saturated with hydrogen atoms a particular fat molecule is. The more hydrogen atoms a fat molecule is missing from being fully saturated with hydrogen, the more double bonds there are within the fat molecule.

These double bonds introduce kinks that change the shape of a “fully saturated” fat molecule from mostly straight to one that has a bend in it.

Saturated fats are generally straight in shape because they have no double bonds within their hydrogen-carbon structure and thus no bends.

I’ve not heard of the term monosaturated or polysaturated or transaturated myself. I think you mean to say monoUNsaturated polyUNsaturated. Monounsaturated fat means a fat that has one double bond so one bend in its hydrogen-carbon structure. Polyunsaturated fat is a fat that has multiple double bonds and thus multiple bends in its hydrogen-carbon structure.

Trans-saturated fats are made by taking unsaturated fats (mono or polyunsaturated) and bombarding it with hydrogen atoms along with a catalyst to remove the double bonds in the hydrogen-carbon structure and turn the mono/polyunsaturated fat into a saturated fat.

The issue with adding hydrogen atoms this way is it fucks with configuration of the hydrogen-carbon structure turning it into a “trans” configuration that our bodies really do not react well to.

Most of our cell walls are made from mono/polyunsaturated fats so those are more useful to our bodies and taking those are generally better for us than unsaturated fats are. Trans fats don’t often occur naturally so our bodies don’t really know what to do with them and kind of throw a tantrum when it sees one.

TLDR; Saturated fats are straight in shape, mono/polyunsaturated fats have one/multiple bends. Our bodies need more mono/polyunsaturated fats compared to saturated fats. Trans-saturated fats are artificially created saturated fats made from mono/polyunsaturated fats and are the devil