By default, the file referred to is in the current directory—the directory from which you run the program. (Or, to use Windows or Macintosh lingo,
this is the current folder.) But you can, if you want, specify a complete path name, optionally including a drive letter. This is all part of the complete
filename—or more precisely, the file specification.
I want to stress on that last sentence, What does it mean "This is all part of the complete filename—or more precisely, the file specification."
A complete path would be:
C:\Some\Folder\On\The\C\Drive\File.exe
Be file specification, I believe it simply refers to the fact that it has an absolute path (no other file can exist with the same path) and that it has it's file extension as well (possibly where the specification part comes in).
I don't believe you should get too worked up over the specifics in regards to technical terms, especially if it's not from a reputable source. The important parts are to understand how it works and what you need to do to make something work properly.