The first of the ten heavenly stems (甲, 乙, 丙, ...). Used to indicate order or parties (e.g., party A in a contract) and in traditional calendrical/astrological contexts.
契約書では便宜上、甲を委託者、乙を受託者としている。
In the contract, for convenience, party A (甲) is the client and party B (乙) is the contractor.
十干の最初は甲（きのえ）で、次に乙が続く。
The first of the ten heavenly stems is 甲 (kinoe), followed by 乙.