Transliteration: 'char sgo
<phrase> "Door of shining-forth" or "avenue through which ... shines forth". Meaning the various ways through which appearances dawn in mind.This seems a very clunky translation, I'll admit, however, there is an important issue. The term འཆར་བ་ q.v. has the specific meaning of that which comes forth from mind into mind. It is not the equivalent of སྣང་བ་ which means all kinds of appearance, including external ones and is used in Tibetan literature specifically instead of སྣང་བ་ to provide an important shade of meaning not embodied in སྣང་བ་. Therefore, although this is often seen translated as "doors of appearance" that is not only incorrect but loses important, often key, meaning.
The term is used in both secular and non-secular literature. In ordinary terms, it simply means anything that comes to mind or a specific thought or train of thought that has come or could come in mind. In Buddhism in general, it is also used with that meaning. In the higher tantras, and especially in རྫོགས་པ་ཆེན་པོ་ Great Completion tantras, it has very special meaning.
In Great Completion, it is one of a series of important technical terms used to refer to the specific ways in which the ground comes into appearance. The ground, which has not come into appearance at first does come into appearance at some point. Because of this, the ground is known as འཆར་གཞི་ "the shining-forth ground" and it has eight འཆར་སྒོ་ avenues through which it comes into appearance are specifically identified. These are the ལྷུན་གྲུབ་ཀྱི་འཆར་སྒོ་བརྒྱད་ eight doors or avenues through which spontaneous existence shines forth.The term is used in a wide variety of ways. See also འཆར་གཞི་ and འཆར་ལུགས་.