lane width
How many bits each value in a SIMD register takes: 8, 16, 32 or 64. The register width divided by the lane width gives the number of lanes.
The lane width is the element size an instruction assigns to each lane (8, 16, 32 or 64 bits); lane count = register width / lane width, so a 256-bit register holds 32 bytes, 16 halfwords, 8 floats or 4 doubles.
See also