The traditionally green coating which protects copper on PCBs from oxidation and shorting due to solder. Use this tag for PCB design questions and soldering questions which require attention to the mask layer.
When soldering BGA devices, an important decision is whether to use soldermask-defined (abbreviated SMD, not the same as "Surface Mount Device") or non-soldermask-defined (NSMD) pads.
Some PCB manufacturers offer minimal spec boards without soldermask.
