"sha" is both the metro code for shanghai (similar to nyc, qla, qsf, was, tyo, etc) and airport code for shanghai hongqiao.

sha metro includes sha (the airport), pvg, and any other airports that might be built later within the shanghai metropolitan area.

when given the choice, most people seem to prefer sha to pvg because the former is closer to town, but as richard pointed out, getting a taxi at sha can be quite an ordeal. furthermore, sha is not all that much more pleasent than shanghai (train) station.