Kanji are logographic characters that originated in China and are shared across Japanese, Chinese, and Korean (CJK) writing systems. Japan officially designates 2,136 jōyō (common-use) kanji for newspapers and official documents.

Kanji have high information density — a single character can convey a complete concept. The 5-character Japanese term "文字数制限" requires 15 characters in English ("character limit"). Kanji dictionaries help look up readings and meanings.

In Unicode, CJK Unified Ideographs occupy U+4E00 to U+9FFF with about 20,000 characters. Including extension blocks, over 90,000 kanji are defined.

For character counting, each kanji counts as one character, but in UTF-8 encoding, each kanji uses 3 bytes. Kanji learning books offer efficient memorization techniques.