You can look at a partition as a high level container of files and directories. Technically speaking, a partition is a contiguous portion of a block device. Partitions of a block device are tracked by a special construct called a partition table.
As a computer powers up, it needs to know where to find its start up code (usually in a “bootable” partition). As a result, the location and format of a partition table depends on the BIOS (basic input/output system) of a system. A PC desktop computer has one way to represent partitions, a Macintosh desktop computer has a different way to represent partitions. Other systems may also have different partitioning methods.