Copper foil thickness is specified in units of ounces per square foot (oz/ft²), or just referred to simply as ounce. Popular thicknesses include 1 oz/ft² (300 g/m²), 2 oz/ft² (600 g/m²), and 3 oz/ft² (900 g/m²). These work out to thicknesses of 35 µm (1oz), 70 µm, and 105 µm, respectively.

It is the copper thickness on the substrate, basically, there are 1 oz and 2 oz available for outer layer. For the inner layer, the copper weight is 0.5 oz by default. 1oz and 2oz inner copper weight is only available for 4 layer boards, besides, 2 oz inner copper weight is only available for 1.6mm.

Notes:

1. For 1 oz board, please make sure the trace width/space is larger than 5mil for 2 layer board, and 3.5mil for 4/6 layer board.
2. For 2 oz board, please make sure the trace width/space of larger than 8mil for 2/4/6 layer board.