Characteristics and use of kanji
Unlike the kana, which are phonetic syllables with no intrinsic meaning, kanji are logographs (also called logograms, pictograms, pictographs or glyphs), meaning "symbols used to represent entire words," or ideograms which represent abstract concepts, such as "up" or "down".
Kanji are typically more complex than kana, have more strokes, and have (unlike Chinese characters used in China), different pronunciations ("readings") depending on how they are combined with other kanji and kana.
A kanji will often have its pronunciation for the given context spelled out in ruby characters known as "furigana," which are small hiragana written above the character (those printed to the side are called kumimoji). This is especially true in texts for children or foreign learners and manga, or for characters not included in the essential kanji set (see below), or for rare or unusual characters or readings.
Kanji have two main pronunciations, referred to as "readings": on readings (音読み or on-yomi) and kun readings (訓読み or kun-yomi). On readings are derived from the original Chinese pronunciations of the character, and are typically used when a kanji is part of a compound. Kun readings are uniquely Japanese readings mostly used to read single kanji, either as complete nouns or as adjective and verb stems. Most kanji have at least one on-reading and one kun-reading each. Kanji also have a third, lesser-known reading called nanori reading, mostly used for people's names.
There are exceptions to these rules. Many kanji have no kun-reading and a few have no on-reading. Some use kun-readings, not on-readings, to make compounds.
Often a kanji will be used for the root of a verb, with the conjugation written in hiragana (in this usage the extra hiragana are called okurigana). When kanji characters are not followed by hiragana they are often grouped in twos and are pronounced in the on reading. The word "kanji"(漢字) is a perfect example of this. Its pronunciation is derived from the Chinese word "hanzi".
Japanese prefers to use the ideographic iteration mark (々) to indicate a plural meaning (pronounced as though the kanji was written twice in a row), whereas Chinese may reuse the first character, or does not indicate plural at all (although the Chinese use is not limited to that of indicating plurality; it is often used in for the purpose of indicating a repetition of a previous character or a group of characters).