[Rattlehead]

If we're talking about a game ie software used for entertainment purposes, then I would say a sim is a game that tries, as near as is possible, to accurately replicate the subject content.

To me, it is more about the idea than the actual execution. Like the old Il-2 for example, is most definitely a simulator for me because the idea behind it was to make a sim that was as close to real life as was possible at the time.
Sure, with many more years of coding and advancement in computing power it could have been more realistic, but at it's heart it tried to be as close to 'the real thing' as was possible without spending an obscene amount of money and time on it.
They still had to make it work within the context of a video game.

By contrast, a game is not particularly bothered with being as close to the real thing as is possible as long as people have fun with it. The entertainment value far outweighs the need to accurately replicate the subject content.
Some aspects may be fairly accurate to the real thing, like for example the 3D models, but the fun factor is king.