Noun
boot sector (plural boot sectors)
(computing) A dedicated sector, usually at the beginning (first sector on first track) of a storage medium, that holds special data used to start a system.
Some systems use a boot block of several physical sectors, while some use only one boot sector. Other manufacturers use the terms "boot block" and "boot sector" interchangeably.
A valid NTFS Boot sector must be present in order to access any data; even if the partition is not bootable. Source: Internet