A PersonalComputer, generally known as a PC, based on an IntelCorporation ExEightySix microprocessor, and designed to run MicrosoftWindows or MsDos. The first version running MsDos was introduced 1981 by InternationalBusinessMachines. Since then desktop Industry Standard Architecture (ISA) computers flourished and have evolved into a Higher Life Form. Nowadays, you can find pretty much any OS you care to mention running on an Intel-based PC of some kind or another.
'PC' is also an acronym for PoliticalCorrectness or PoliticallyCorrect.
The most important thing about the PC is that it is an open hardware standard that anyone can implement. This means it is easy to find replacements for any part of the computer at any price point, making it impossible to get locked to one specific hardware vendor.
[NOTE: this argument is left in place for historical reasons only. We all love a good rant, even when it's a decade or more out of date.] The downside is that standards compliance is not perfect and so we constantly get stuck with lowest-common-denominator de facto standards based on the most ass-backwards hacked-up piece of crap version of the component our software might still come across. An example of this is how difficult it can be to even find out how much hard disk space exists on a given system in the face of absurdly small size limits hard-coded into the lowest-common-denominator interfaces to the hard disk drive.
On the plus side, PCs are cheap and everyone sells them and components for them. It was the explosion of 32-bit PCs, the first models that could run real operating systems that depend on a hardware MMU, in the late 1980s and early 1990s that sparked the FreeSoftware and OpenSource Unix revolution.
History
The IBM PeeCee was not the first IBM machine to arguably qualify as a PersonalComputer, but it was the first of them to be a major success. IBM was the quasi-monopolist of business computing at the time, and its core business was its dominant share of the MainframeComputer market. It had seen the personal computer as either a toy or as a potential squeeze on its MainFrame business. By 1981, though, the business market for personal computers was starting to take off without IBM - the AppleIi had its KillerApp in VisiCalc, and DeeBase? was out for ControlProgramMonitor? machines - so the company decided that it needed its own. In technical terms the original IBM PC's (somewhat-)16-bit Intel 8088 MicroProcessor? outshone chips like the AppleIi's MOS 6502, but the PC's graphics, sound and overall design were fairly unimpressive even by 1981 MicroComputer standards. (Though the keyboard was exceptionally good.) But it was the first personal computer with the IBM imprimatur, and at that time NobodyEverGotFiredForBuyingIbm?. (and besides, graphics are only for VideoGames) As widely expected, the PeeCee greatly expanded the PersonalComputer market and came to dominate it. But it didn't happen exactly as IBM intended it to.
The PC was quite an open system in hardware and software terms, certainly by IBM's standards. It had been built quite quickly using many off-the-shelf components, also unusual for BigBlue at the time. They included IntelCorporation's processsor and MsDos, a ControlProgramMonitor?-clone OperatingSystem provided ad hoc by MicrosoftCorporation, both on non-exclusive terms. IBM thought it could control the PC platform quite well through its elaborate and proprietary BIOS. In fact the BIOS was soon ReverseEngineered and IBM PC clones were released. This did wonders for the PeeCee platform in the market but cost IBM its control over what had become a de-facto standard. Without control of the PeeCee, and hence the PersonalComputer market, IBM lost the ability to protect the MainframeComputer from PersonalComputer competition by gaming the price and features of the PeeCee. IBM tried to regain control, but the horse had bolted. The upshot was that WinTel gained control of the PeeCee platform, the mainframe lost its dominance faster than it might otherwise have, and IBM lost its monopoly. By 1993 it had became a struggling computer company with a loss-making commodity PeeCee business. (Although it had notable successes with its ThinkPad NotebookComputers.) A rather changed IBM returned to profit, and sold its whole desktop and mobile PeeCee business to LenovoGroup? in 2005.