This is the cast type skill for rift spells.
The in game help reads:
Skill duration: random. Type of skill : spell casting skill (arcane skill). Affecting stats: None. It uses no endurance points. This skill lays the groundwork for all spells which manipulate cross-dimensional energies, and beings. Even the most accomplished Riftwalker does not disregard the knowledge gained from these simple, but foundation-forming abilities. The guild has a saying "Disregard the simple, and simple you shall remain".