Afaik the correct definition is given by Halley, the letters must form a word. Merely being pronounced like a word, for example SCSI isn't sufficient. There are also 'contracions' which are one step short of abbreviations, for example COINTEL. Technical English says an abbreviation should be written with periods as separators, for example I.B.M. or with an appended period as in Mr. and Ms.
The only answer to catching and mapping all these shortened forms is a database/list of some kind. The Oxford dictionary used to have several pages devoted to them, but I think these days there are so many from specialised fields that no-one bothers to compile them anymore. btw Lug, also = Linux User Group and an kind of knot. My most hated confusing acronym is LOD in games design which is 'level of detail' and 'last object drawn' in the engine and 'land object down' in terrain building.