a prefix used to mean “same.” We can stick iso- in front of a lot of different terms that we also stick hypo- (below) and hyper- (over) in front of (e.g. isotonic, isoosmotic). But iso- can be put in front of a lot of other words too. For example, “nuclear isotopes” refers to versions of the same element that have different numbers of neutrons (P.S. some isotopes are radioactive). Another common place you see “iso-” is “isomers” which refers to molecules that have the same components (e.g. same atoms), but arranged differently – such as different arrangements in linkages (structural isomers) or same linkages, but different arrangements in 3D direction-stick-out-ing.
Another place you’ll see it is the “isoelectric point” (pI) which is the pH at which a protein is neutral overall. Different proteins have different pIs & you can take advantage of which is a technique to separate proteins based on charge by sending proteins traveling through an immobilized pH gradient & letting them travel towards the opposite charged end until they reach their “isoelectric point” at which point they have no motivation to go further because there’s no “opposite” to be attracted to! So, a way to help remember iso- is “I so” don’t want to go.