The meaning of the English idiom "pot calling the kettle black"

WiseGeek.com says:

The term “the pot calling the kettle black” is usually used in the sense of accusing someone of hypocrisy. The origins of the phrase date back to at least the 1600s, when several writers published books or plays which included wordplays on this theme. Despite suggestions that the phrase is racist or nonsensical, the meaning is actually quite obvious when one considers the conditions of a medieval kitchen.

Typically, pots and kettles were made from heavy materials like cast iron to ensure that they would last and hold up to heat. Cast iron tends to turn black with use, as it collects oil, food residue, and smoke from the kitchen. Both pots and kettles would also have been heated over an open fire in a kitchen. As a result, they would have become streaked with black smoke despite the best cleaning efforts.

Since both are black, the pot calling the kettle black would clearly be an act of hypocrisy. The act could also be described by “it takes one to know one,” and it suggests a certain blindness to one's personal characteristics. There is another explanation for the term, involving the pot seeing its black reflection reflected in a polished copper kettle. In this sense, the pot does not realize that it is describing itself.

One of the earliest written instances of the phrase appears in Don Quixote, by Cervantes. The epic book was published in the early 1600s, and had a big influence on the English language. Numerous terms and idioms have their roots in Don Quixote, such as “quixotic” to describe an idealist. Shakespeare also played with the concept in one of his plays, as did many of his contemporaries. The phrase has been twisted and expanded over the centuries, appearing in forms like “pot, meet kettle.”

Some people believe that the phrase is racist, since it refers to the surface color of the objects involved. These individuals might want to keep in mind that in a modern kitchen, the idiom might be “the pot calling the kettle silver,” in a reference to the fact that many modern pots and kettles are often made from polished stainless steel. In this particular instance, skin color has nothing to do with the idiom, except in the sense that both of the objects involved are the same color.

Phrases.org.uk defines its meaning as:

The notion of a criticism a person is making of another could equally well apply to oneself

WiseGeek, the source of Benyamin Hamidekhoo's answer, rightly notes that both the pot and the kettle "turn black with use." That is, they start out a silvery or grayish or coppery color and gradually turn black through exposure to the heat and smoke of the fires or heating elements that they are set above. However, I disagree with WiseGeek's contention that the essential meaning of the saying would be preserved if it were reworded (for the modern sanitary kitchen) as "the pot calling the kettle silver." In my view, one crucial aspect of the original saying is that, in the world of anthropomorphic pots and kettles, being black is an undesirable trait—and that calling a receptacle black, even if the receptacle's blackness is incontestably true, is an insult. Without the element of insult, we might as well have a saying about "the apple calling the strawberry red"—which we don't.

The metaphorical idea at play here is that a clean pot or kettle is like an uncorrupted person, but that through exposure to "blackening" elements—or even perhaps to day-to-day life—the receptacle's original color, like the person's innocence, is lost. It is deeply hypocritical for one receptacle (or person) to criticize another for possessing an undesirable characteristic that (in truth) both of them possess. And as with the blackness of the pot and the kettle, the corruption of both the accuser and the accused doesn't make the accusation of corruption any less of an insult. Having said that, I do share WiseGeek's view that the saying has no intentional racial overtones.

The saying is rather pessimistic, it seems to me. After all, what is more natural than that a pot and a kettle—without the intervention of some vastly more powerful being in the scullery—should turn black in the course of their duties? James Branch Cabell points out something similar with his apothegm: "A man's hands are by ordinary soiled in climbing."

The idiom or something like it is attested in writing as early as 1620

The pot calls the pan burnt-arse (1639).

(Oxford Dictionary of English Proverbs;
The 1620 citation is attributed to Shelton's Don Quixote translation.)

I am from the US and I learned the expression from my mother at the age of 8--10 therebouts.

Saying in Ireland; the "Kettle calling the pot black arse" means simply that the very fault you accuse the other of, you have yourself. The kettle and pot are both black from the open fire/cooker.