壱 (readings: いち, いつ, ひとつ; Japanese kanji) means “One (in Documents)”. It is a Jōyō kanji taught in Japanese secondary school (junior & senior high) — the 高手 · Master tier beyond the grade 1–6 Kyōiku set, and appears in words such as 壱万円 (ten thousand yen, formal).
What does 壱 mean?