This confusion is especially annoying when trying to purchase a bootloader unlocked phone on secondary market. I'm not even sure it's possible if you buy through a dealer. By unlocked they exclusively mean carrier unlocked.
It is still shipped locked. Unlocking wipes the device.
It also doesn't work if your device is carrier locked.
Bootloader unlocked generally means that the vendor permits the execution of arbitrary operating system code, ie there is no jail to break out of.
In fact If I saw jailbroken in a listing I'd assume it's because the device cannot have its bootloader unlocked.