you could have come across .nfo files in your downloads probably when you download from torrents a file withe extension .nfo downloads and you don't know what to do with it when you open it you normally get a error like this:
.nfo file is short form of info or information to open such files you have to open it using note pad it normally contains the information about the file which you have downloaded how to install that file etc probably the information in the .nfo file gives the details necessary to use the file
