[stuporglue]

A live image is an operating system image which you can boot from and use vs. an install disk which can only install, but there's no usable environment available).

A reproducable build means you can get the same source code and compile it, and it will be identical to the published image. This is important because otherwise you don't know if the published image actually used some other source code. If it used some other source code, the published image might have a backdoor, or something that you can't find by reading the source code.

[perdomon]

Is that the idea behind Tails OS? It runs from removable media and disappears when ejected?

[abdullahkhalids]

Yes. Though the disappearing doesn't happen when you eject the removable media. When you first boot from the removable media, the OS loads itself into the RAM. If you want to open additional programs, then those are loaded from the media into RAM and then executed. However, you can remove the media at any point after boot, and after that you only run the programs that are already loaded into RAM.

Also we have had live images of various OSes for many decades. I seem to recall that we used to load DOS from floppy disks.