Some device manufacturers (including Samsung, HTC, and a few others) use the term “Download mode” instead, but the functions are relatively the same.
Luckily, most bootloaders can be unlocked, which allows you to then flash new software. Most Android devices come with locked bootloaders – i.e., you can’t alter what it does.
Bootloader – When you power on a device, the first thing that turns on is the bootloader, which is responsible for starting up other processes.