I pop in from time to time on several forums related to FI, simple living, frugality, minimalism, etc. This topic comes up a lot. I'm always amazed at how hung up people get on labeling and trying to fit in to some label definition, or fit others in.
There is no universal definition for any of these terms. Even terms like "want" and "need" have a lot of grey area. I have a friend who keeps his thermostat at 50 degrees during harsh Colorado winters, and wears heavy down coats around the house. I prefer the heat up a little higher, but label that as a need, because I am uncomfortable going about my day when I'm that cold. He doesn't; it would be a want.
There are two ways to define these terms - first, you can define what they mean to you based on your passions, desires, beliefs, goals and background. So, I find it frugal finding a good deal on grass-fed, organic , free pasture-raised meat if buying it fits within my budget/financial plan, and given my belief that factory farms are evil and my desire to not support them. Second, you can define them by comparison with other people. So, with the same meat example, I may not be "frugal" anymore, because another "frugal" person would eschew the expensive meat, instead paying pennies in comparison for cheap, low-quality factory farmed meat. I'd rather not define my lifestyle choices based on what another person does. It's just 'keeping up with the Joneses'. It also opens us up to being judgmental - I have a friend who lives pretty frugal, due to a low paycheck and lots of debt, but he has cable. I know a lot of "frugal" people who would tell him he's not frugal and he needs to cut the cable if he wants to be frugal, and attack the debt. The fact is watching TV is his total passion and major form of recreation, so it's an expense that he budgets for because it brings him joy, even if it means working a little longer to pay off his debt. I may find that strange, but I have to admit, he finds reasonably good deals, he budgets for it and it brings him joy, so who am I to judge or label his choice?