[Q] Can you please explain what is the ROM? topic

Hey, I have really basic information about computers and OSs so I really need some explanations for the case of android smartphone (qualcomm mainly). So let me tell you first what I know (I hope that this is true): For a computer they use EEPROM and it's a type of ROM which is erasable. The bios is stored there and it's the first thing loaded when starting the computer. (It's is easily updatable as I have already updated my bios). For the case of android smartphones I think that they use NVRAM, but I don't know what is NVRAM physically? is it a build-in memory separated from storage devices like on computers?! or is just a partition of internal storage? (internal storage I mean /dev/block/mmcblk0). I found that NVRAM can only be erased using JTAG on some websites but I found that device cloning is done copying mmcblk0 from one phone to another, so that means that NVRAM is located in mmcblk0. And if NVRAM is just a part of mmcblk0 so why is it a read only memory? we can easily write to other partitions, so why not NVRAM?! I'm really confused...

Please share your knowledge, I really need years of studying electronics and computer science to know all this by myself... Thank you all!!