Furigana are a reading help printed next to kanji in Japanese text to indicate their pronunication. They are generally written in hiragana, but can occasionnally also be written in katakana or romaji.
They are used to assist children, students, or non-native speakers in reading unfamiliar or difficult characters. They can also be used to indicate the reading of kanji that are not in the list the most common kanji (jōyō kanji) or to indicate the pronunciation of proper names.