From LQWiki

Files are nothing but stored data streams. Only one stream per-file. In such a stream you may read, write, and seek, but not necessarily all at once. Some files are not capable of seeking. Some files may only be readable, or only be writable. This was exploited in the kernel to implement pipes and devices, thus the saying "everything is a file".

Files contain a set of permissions and attributes. These are used to store if a file can be read, written and executed. Also, if the filesystem supports it, extended attributes may be present. Extended attributes are obviously not part of the original unix design, but useful. They are essentially arbitrary name:value pairs attached to a file, typically used by advanced security systems in the OS.

You can find out the type of a file using the command

ls -l

The file type can be

• ordinary file
• directory
• link
  • hard link
  • soft link
• socket
• pipe
• device
  • block device
  • character device