What is BIOS in the computer

After to be start to computer, first of all -what screen looks that is called BIOS(Basic input output system). Added with these motherboard, is a firmware or software- what helps to computer in to(operate or start). Without this - computer can not run, anytime. In the computer, in the memory - during loading to operating system, then BIOS runs to POST(Power on self test)system hence that every part of hardware or software are working, correctly, yes or no. This is because of [(to be start of POST(Power on self test)]. After this, our computer runs any program.