Yin is the diametric opposite of Yang. It embodies concepts such as spirituality, the mind, creativity and/or the imagination. Going back to my example of how any physical action produces physical energy, any action of the mind produces spiritual energy. Yin Release is the capacity to harness that energy. Because of those roots, all Yin Release techniques manipulate the spirit, or the mind, in some way. Or at least, they rely on that connection to produce an effect. Take Hungry Ghost, which produces a spiritual tether to an enemy and weakens them through that tether. Or Hands of Sloth, which slowly weakens and eventually seals away an opponent's mind, the central domain of their spirit in a sense. On the note of spiritual/mental subversion, Yin Release also has a connection to Genjutsu. Illusions bolstered by Yin Release are generally far more potent than ordinary Genjutsu, since the field allows for more direct manipulation of an opponent's mind/spirit, as well as just the potency of Yin Release chakra. Such Genjutsu can break through passive defences or immunities, and can even lock off particular methods of Genjutsu break.
I don't think any Yin techniques outwardly describe the nature of spiritual energy in terms of its basic characteristics, but if I had to attribute any to them, it would be that it's cold. Opposite of Yang and all.
Back to its effects though, the last of them being related to Yin as a domain of the imagination. There are a few techniques which take advantage of this characteristic, one of them being Yin-Yang Release. The first two are Change into Heaven and Great Phantom Dragons. Both of these techniques entail the use of Yin Release to alter the physical characteristics of a technique according to their imagination. In the case of CiH, it's a targeted use, whereas the Phantom Dragons themselves are the object of alteration. A key difference between them is that CiH cannot change the fundamental nature of a technique, only its physical properties (such as turning energy solid), while the Phantom Dragons can be turned from constructs of spiritual energy into different elements that the user knows. The last technique, Creation of all Things, probably best embodies the use of Yin Release as a conduit for the user's imagination, as it involves the application of Yin Release to create a physical object that possesses whatever characteristics one so desires.
That should be it. Besides the ability to absorb/siphon chakra, which is a property unique to Hungry Ghost and Phantom Dragons.