A file system (also filesystem) is a software mechanism that defines the way that files are named, stored, organized, and accessed on logical volumes of partitioned memory. File systems are designed to store folders, system and data files, and metadata on storage media.
"[A]ll filesystems share some common traits. First, they use the concepts of directories and files to organize and store data. Directories are organizational structures that are used to group files together. In addition to files, directories may contain other directories called subdirectories. Second, filesystems use some data structure to point to the location of files on media. In addition, they store each data file written to media in one or more file allocation units. These are referred to as clusters by some filesystems . . . and as blocks by other filesystems."