Recirculating Infusion Mash System (RIMS) is a brewing system where you use one to three kettles to brew beer.
The mash water is heated, transferred to the mash tun, and then either heated in the mash tun or run by a heating element that comes into direct contact with the wort. Finally the grains are either removed from the mash tun and the wort boiled there or the wort is transferred into a boil kettle.
Your typical all in one brewing systems, such as the Speidel Braumeister, the Brewtools B40, the Grainfather and the Robobrew BrewZilla are all variations of a RIMS system.
The main difference between a RIMS and a Heat Exchange Recirculating Mash System (HERMS) is that the heating element in the RIMS comes in direct contact with the wort while the heating element in the HERMS doesn’t.