I know I've mentioned before that kanji is not a language. It is not the name of the written Japanese language. (The name of the written Japanese language is "Japanese". Or "nihongo" if you want to get self-referential about it.)
So what's kanji? Let's see the definition a Google search returns:
A system of Japanese writing using Chinese characters.
Er... NO. Kanji is not "a system of Japanese writing". That's the mistaken definition you get from Google – and from Dictionary.com and Answers.com and Merriam-Webster.comand who knows how many other sources, all parroting the same wrong answer.
It's no surprise, then, that so many people believe this same mistake. Look at a single page from Yahoo Answers, collecting responses to the question "what does the word kanji mean?":
Kanji are Chinese words used in the Japanese language.
Hmm. Not the worst possible answer, but not right either.
Kanji looks exactly the same in both Chinese and Japanese...
Sometimes, but not necessarily.
...but depending on which language the word is used in, the meaning of the word are completely different.
Sometimes, but not necessarily.
Kanji can mean either the japanese writing system as a whole...
NO!!!! Absolutely not.
Think of it as "alphabet" and/or "letter" and you won't be far from the intended meaning most of the time.
"Alphabet" and "letter" really aren't right.
Kanji is a system of Japanese writing using Chinese-derived characters.
So much wrong in so little space. Kanji must be a really nuanced, esoteric concept to struggle with, right?
No to that too. The real definition of kanji is ridiculously simple.
Would the real kanji please stand up?
Let's turn to Wikipedia, which, ever-present jokes aside, is actually a wonderfully reliable source for factual matters. Its definition of kanji:
Kanji (漢字) are the adopted logographic Chinese characters that are used in the modern Japanese writing system along with hiragana (ひらがな, 平仮名), katakana (カタカナ, 片仮名), Hindu-Arabic numerals, and the occasional use of the Latin alphabet. The Japanese term kanji (漢字) for the Chinese characters literally means "Han characters" and is written using the same characters as the Chinese hanzi (simplified Chinese: 汉字; traditional Chinese: 漢字).
YES. That's a bit wordy, with more information than is needed for our purposes here. Allow me to reword it:
Kanji is the Japanese word for "Chinese character(s)".
That's it. "Chinese character(s)", for a plug-simple, two-word definition. The whole set of Chinese characters, or just some. The couple thousand that are taught to students in Japan, or the many thousands more found in Chinese texts. Or the lone, lopsided, 鮪 that's translated as "NINJA CLAN HONOR" in the Little Rock shopping mall tattoo booth but actually means "tuna". They're all kanji. Should anyone sidle up to you and ask, "Say, good-looking and urbane reader of Home Japan, what are kanji?", just reply "Chinese character(s)", and you'll be dead on the money.
As you can discover in a deeper discussion of Chinese characters, that "logographic character" business is what makes the labels "alphabet" or "letter" less than ideal. If you want a solid English word to use in discussion, a simple "character(s)" will do fine. And do note another important point from the Wikipedia excerpt above: Chinese characters are one character set (or script, if you will) that, along with other character sets, is used in the Japanese writing system. Which is ONE, SINGLE, Japanese writing system, even if it uses multiple character sets (as does probably any other language you can think of).
The Chinese character set is also used as part of the Korean writing system and the Vietnamese writing system – even if, as I understand it, the characters see far less use in those writing systems than they do in Japanese. The Chinese character set is a major part of the Chinese writing system, though (something that I hope didn't need to be said).
So. Those Chinese characters do get around a bit! But whether you call them kanji in Japanese or hanja in Korean or Chữ Nôm in Vietnamese or hanzi in Chinese or "Chinese characters" in English, know that these characters are part of several writing systems, but are not a writing system in and of themselves.
That's it. Easy to understand and good to know!