Gnosis simply means knowledge in Greek.
In the context you used it, gnosis is esoteric in nature: it is the knowledge necessary to achieve enlightenment/perfection (salvation) that is hidden from the vulgar common herd, made available only to members of a closed group of initiates. This is the sense in which “gnosis” is used in the mystery schools of antiquity and by the thinly-Christianized Gnostic sects of the early Christian centuries. The principle of gnosis receives a rebirth/reinvigoration within freemasonry and other such secret societies.