A file system is a structure of directories that is used to organize and store files.
The term file system is used to describe the following:
A particular type of file system: disk-based, network-based, or virtual
The entire file tree, beginning with the root (/) directory
The data structure of a disk slice or other media storage device
A portion of a file tree structure that is attached to a mount point on the main file tree so that the files are accessible
Usually, you know from the context which meaning is intended.
The Oracle Solaris OS uses the virtual file system (VFS) architecture, which provides a standard interface for different file system types. The VFS architecture enables the kernel to handle basic operations, such as reading, writing, and listing files. The VFS architecture also makes it easier to add new file systems.