"Hapspir, Barrini, Corbolan, Triaxis" was a high-level (K-12) recognition code used by Imperial covert forces during the time period after the Battle of Yavin up to the Battle of Endor. Its full use identified the user as an undercover Imperial Agent, that is, an individual in direct service to Palpatine, although use of the first two terms identified a courier from a Grand Admiral. The full code, with the use of all four terms, was used to confirm an agent's identity to those of captain rank or higher, while the first two terms alone were used for those of lower rank, such as stormtrooper squad leaders, and civilian officials.
Mara Jade most notably used this recognition code throughout her career, although it did not seem to be specific to her, as it did not identify her specifically as the Emperor's Hand. Later she would use it to encourage the captain of the Adamant to ferry her to Grand Admiral Thrawn. The captain of the Adamant was sufficiently impressed with the code not to imprison her, but the Grand Admiral felt that it was insufficient proof of her identity, suggesting that the security of the code might have been somewhat compromised in intervening years.