The Stratum protocol is used for pooled mining as a replacement for the obsolete getwork protocol. The details of the specification, as provided in many places, have be gathered here: Stratum protocol documentation The original mining service specification was available on Slush's pool website. Other examples are available on BTC Guild's website. See also on the forums and the official site. Stratum is also a proposal for an open source client-server "Overlay" protocol that enables thin clients (currently used by Electrum client).
Tables showing miner/server support for Stratum mining protocol:
|Server||get transactions||dynamic difficulty||job frequency||resume|
|HHTT||No||No (User selected difficulty)||30s||No|
|50BTC||No||No (User selected difficulty)||5s||No|
|Ozcoin||No||Yes or user selected||30s||No|