In Buddhist Pranama (epistemology), there are two generally accepted categories of valid cognition: (1) direct perception and (2) inference.
Within direct perception (Sanskrit: pratyaksa) there are four sub-categories: sensory direct perception, mental direct perception, yogic direct perception and reflexive-awareness direct perception.
Yogipratyaksa is the Sanskrit term for Yogic Direct Perception, and is defined as an unmistaken non-conceptual cognition arising on the basis of shamatha and vipashyana. In other words, Yogipratyaksa is a form of direct perception rooted in meditative awareness. It can have an apparent object (e.g. in the case of being able to see something which is hidden to normal perception), or no apparent object (e.g. when "seeing" selflessness or impermanence directly, as a fruit of meditative wisdom). More metaphorically, Yogipratyaksa can be considered as a form of “mystic intuition.” It's a kind of "apperception" which is free of conceptuality, is apprehended on a level of pure immediacy, and is an absolutely trustworthy (as opposed, for instance, to sensory hallucinations) and reliable cognition.
Unlike sensory direct perception or mental direct perception -- which all ordinary beings have access to, and which are only conventionally valid -- Yogipratyaksa is ultimately valid, i.e. is a form of cognition through which one is able to realize the true nature of phenomena.
See Also: The Three Natures