Final answer:
A primary partition is used to store and boot an operating system by default. It is distinct from extended and logical partitions and can be set as the active partition for booting the system.
Step-by-step explanation:
The term that describes a partition used to store and boot an operating system by default is a primary partition. In the context of disk partitioning, the primary partition is one of the partitions on a hard drive that the BIOS or UEFI firmware can use to boot an operating system. This should not be confused with the system partition, which might only contain the bootloader or system files necessary for booting, but may not actually contain the operating system itself.
A hard drive can have up to four primary partitions or three primary partitions and an extended partition, which can then host multiple logical drives. Unlike the latter two, primary partitions can be set as active partitions to boot the system.