A computer file is a block of arbitrary information, or resource for storing information, which is available to a computer program and is usually based on some kind of durable storage. A file is durable in the sense that it remains available for programs to use after the current program has finished. Computer files can be considered as the modern counterpart of paper documents which traditionally are kept in offices' and libraries' files, and this is the source of the term.
In modern computer architectures, files are organized in a tree structure. On the top, you have a root like C:\ in windows systems. There are several subfolders (inner nodes) below the root, e.g. Program Files or Users. The computer files, which contain the data, are the leaves of that tree.
On unix based systems, many types of system information are also represented as files, in filesystems such as sysfs and devfs, even though they don't represent information on a durable storage medium.
directory, folder, stream, filesystem, block, file-io