PC-DOS, standing for Personal Computer Disk Operating System, is OS made by IBM for its personal PCs. However, its actually based off MS-DOS, that is based off 86-DOS.
By 1981, IBM has found out that PCs can be not just gigantic machines taking up entire rooms made for huge corporations, but also small "micro computers" made for home users. IBM decided to develop one, that was called IBM Personal Computer, IBM PC or IBM 5150. The PC was pretty weak: 4,77 Megahertz CPU (Which is Intel 8088. For comparison: My laptop has a processor with 2600 Megahertz or 2,6 Gigahertz.), 16 kylobytes of RAM (Can be extended to 256 Kylobytes yet thats still just nothing. My laptop has 8 gygabytes of RAM right now.) IBM PC didnt even have a hard disk, instead there was Two slots for Floppy Disks (its not the 1,44 megabyte ones you know. It was 160 kylobytes floppies) where into one slot you would put a floppy disk with operating system, and into another you would put floppy disk with a program you need.
But this is IBM PC, what about PC-DOS? Well, you cant just create a PC and thats it. It also needs an OS. IBM litteraly stands for International Bussiness Machines. Weird name for a company working on a personal computer. But IBM knew a little company called Microsoft, by its name you would understand its working on software for those. IBM knew them because they made Microsoft Basic. IBM decided to let Microsoft develop Operating System for its PC. And Microsoft stole another DOS (86-DOS that you can download at Other DOS page), remade it a bit and called it MS-DOS. But it was buggy. Microsoft tried to fix the bugs, but IBM decided to fix them itself as well. IBM in the end rebranded it as PC DOS.