Following are few extensions of shapefile;
My questions are;
1) When would .fbn and .fbx files will be created in shapefile? What are read only features of shapefile?
2) When would .ain and .aih files will be created in shapefile?
Any help is highly appreciated.
wikipedia source and one other reference give mention to the first 2. They aren't documented in the original 1998 description referenced here as well using almost the same words...perhaps the same writer and also duplicated in help files. A 2002 refers to them 21456 - What are all the file extensions related to ArcView? for read only datasets...a slightly different connotation. If might be worth, as a lark, using the operating system to make a plain shapefile readonly, then create an index and see if they are created. In any event, other links can be found in these two links etc etc
ESRI Shapefile contains a nice concise description.
GeospatialPython/pyshp · GitHub has other information