From China Digital Space
暂住 (zàn zhù): temporary residence
This refers to temporary residence permits currently needed for out-of-town visitors and workers in twenty-one cities (according to Wikipedia, as of July 2010). Those in cities without a temporary residence permit are fined or deported. The temporary residence permits are of questionable legality because a similar national system of temporary residence permits have been abolished and many scholars find cities’ current systems of temporary residence permits to be unconstitutional. This is perhaps one reason for a trend in abolishing temporary residence permits. However, notable among those cities that retain the system of temporary residence permits are Beijing and Shanghai, which claim the permits are necessary to impose order. Some cities have changed the name of the permits from "temporary residence permit" to "residence permit" while retaining the same basic system.