The eight leading characters of the 聖行 chapter in the Nirvāna sūtra 生滅滅巳寂滅爲樂, the teaching of the sūtra is death, or nirvāna, as entry into joy.

A Dictionary of Chinese Buddhist Terms, William Edward Soothill and Lewis Hodous

（雜名）涅槃經聖行品所說之生滅滅已寂滅為樂八字也。謂之雪山八字。三教指歸二曰：「雪山八字者，即聖行品，雪山大士從羅剎求半偈而捨全身也，八字即生滅滅已寂滅為樂。」涅槃經十四曰：「誰當信汝如是之言，為八字故棄所愛身。」

丁福保《佛學大辭典》