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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.

I understand it to mean that a person is guilty of the same thing she is accusing another person of, often in greater degrees than the accused, and so has no right to be derogatory to him. I like Wikipedia's synopsis: "As generally understood, the person accusing (the "pot") is understood to share some quality with the target of their accusation (the "kettle")." It also has the connotation of hypocrisy. Wikipedia gives a list of similar phrases, parables, and stories in English and other languages, such as the ancient Greek concept of "the Snake and the Crab," and the phrase, "those that live in glass houses should not throw stones."

I best like the explanation of the origin by commenter mark on answers.yahoo.com. He points out that regardless of whether the kettle is seen as black (as the pot is black) or polished metal, "for one to accuse the other of being black points out ignorance of oneself in accusing another (sort of, it takes one to know one)."

These are all common English words, so I would not find it difficult to read or pronounce. This question seems to have value only in comparing it to other idioms.

This idiom would only be used in informal situations. It often is used jokingly, but can be construed negatively, so one would want to have some familiarity with the listeners before using it. Our family has a variation we say to each other when one complains about something that is at least partially characteristic of the one complaining: "Hello pot, meet kettle!" I also sometimes use a variation of it to soften the impact when pointing out a problem with someone else: "I say this as a pot talking to the kettle" -- indicating that I am not being derogatory about the person, as I am guilty of, or perhaps struggle with the problem also.

I am a college-educated professional who works in the area of Information Systems (computers).

Apparently among the internet generation today, it is sometimes shortened to "pot, kettle, black." See also yahoo link above and the definition on the internet's Urban Dictionary.

I felt quit difficult with this idiom when I heard it for the first time. But I realized the right meaning of this idiom. This idiom focuses on those who tries to hide their own faults and blame others for their mistakes. There is no right for that man who blames others without correcting himself. It is very easy to blame others. But before that one should check himself/herselves whether he/she is right or not.