If Avast comes up with it as a bad file, kill it, it does not sound like anything usefull. API is a real term though, and I'm sure many applications use that word in their files, but your specific file does not turn up anything usefull and a few api files in Windows are marked as known viruses.
About what lives in the Windows folder, because Windows is such an open system, it's hard to say what files you will find in there especially once you start installing applications. Asking here or just doing a web search on the file will get you an answer though.