The invention relates to a turbine, in particular of an exhaust-gas turbocharger, comprising a turbine rotor which is supported rotatable in a housing, and to which at least one guide vane apparatus forming a radial inlet channel for a medium driving the turbine rotor is allocated, wherein the guide vane apparatus comprises a guide vane mounting ring with a plurality of guide vanes which radially surround the turbine rotor and which are located within the inlet channel, as well as a guide vane cover ring, and wherein the inlet channel is axially bounded by the guide vane mounting ring and the guide vane cover ring, and the guide vane cover ring abuts with a front side facing away from the inlet channel against a support area of the housing. The invention provides that the housing (5) comprises in the support area (15) at least one recess (17) which is open-edged towards the guide vane cover ring (9), and through which the medium can flow.Furthermore, the invention relates to an exhaust-gas turbocharger, in particular for a motor vehicle, comprising a compressor and a turbine which are actively connected with each other in a mechanical manner.