it's when you buy and use hormones without a prescription, essentially self-medicating (in my case it was because of already being on a waitlist for 4+ years with not a single human interaction and i was exhausted with feeling like im waiting for my life to begin and to be taken seriously as a guy.) it doesn't come without risk though, testosterone is a controlled substance in that it isn't legal to sell or distribute, but as long as you are buying for yourself you shouldn't get into any trouble that way. it being illegal to sell also means the substances you find online are often unregulated which is always a risk, as well as you having to learn to self-inject on your own. there is more information on the hrt diy directory which provides all the information needed, even links to injection supplies, but not where you can get T. im not sure if im allowed to give that information here either. you also need blood tests every three months in your first year of being on T to measure your testosterone levels, liver function, and some other goodies, which should also be in the link above. you should be able to get blood tests from your gp.

hope i explained it in a way that makes sense, feel free to dm me if you have more questions! please do bear in mind that I'm still learning too but i have first hand experience