I believe LOC stands for the level of consciousness. Thus C stands for Consciousness.
Th purpose of a secondary assessment is to identify and care for conditions that are not life threatening. Other objective may be to conduct a more thorough examination than in the primary assessment, also identify and treat any missed life threatening conditions among others. The basic assessment includes the level of Consciousness, response to verbal stimulation, A.V.P.U, responsive to painful stimulation, GCS, LOA, and unresponsive to painful stimulation.