Ok, maybe I'm too lazy to do a thorough search on what it is. Before I posted this question I searched forums and Google for a definition, and all I got out of it was that with a locked bootloader you can't install custom ROMs. Seein as I had a Motorola Cliq before, and how they were on that BS with that 2.1 update, there were custom Eclair ROMs. Which kind of contradicts what I thought a locked bootloader was. So I thought I'd just ask for a more direct answer. So in short, i thought it meant you can't install custom ROMs, but I feel that isn't exactly what it means seeing that the Cliq had custom ROMs for it.