LBA is Logical Block Addressing.

Early PC hard drives were supported by the PC BIOS using Cylinder/Head/Sector addressing.

To read or write from a specific sector on the disk, you specified the sector in terms of its cylinder number, its head number, and its sector number.

LBA adressing uses just one number. In LBA addressing, the first sector on the disk is sector zero and all sectors on the disk are simply incremented from there.