A set of runes that appear in the Ico video game. Each specific rune corresponds to a letter in the English alphabet, usually derived from the first letter in the word that the rune is a picture of (for example, the rune for "A" is a picture of an ant.)
In the first playthrough, Yorda's speech is subtitled with these runes instead of English, but her speech is subtitled in English on a subsequent playthrough.
In-universe, it's the alphabet used for the language that Yorda and The Queen speak, which is different from the language Ico speaks.