I understand 1x 2x 3x 4x but what exactly is 2-2 4x.

2.4x is also a recording speed that was used for DVD+R discs only. I think the transfer rate for 2.4x recording was 3.240 KB/s. The first DVD+R discs were certified for 2.4x, then came 4x, 8x, 12x, 16x.

2-2.4x

DVD-R’s burn at 2x

DVD+R’s burn at 2.4x

It’s a all-encompassing statement: will burn 2x or 2.4x.