The combination of a riser support template and the associated piping and connections for the riser and pipeline(s) is also often referred to as a riser base.
Source: API RP 17A, Design and Operation of Subsea Production Systems—General Requirements and Recommendations, Fourth Edition, Reaffirmed 2011. Global Standards
Riser bases are used to connect flexible risers to flowlines, and may also be required to support subsea buoy/arch systems (e.g. steep-S configurations). The riser base can be either a gravity structure, a piled structure or a suction/anchor pad.
Source: API RP 17L2, Recommended Practice for Flexible Pipe Ancillary Equipment, First Edition, March 2013. Global Standards
Structure positioned on the seabed, used to provide a structural and pressure-tight connection between a flexible riser and a flowline. NOTE 1 See 4.4.8. NOTE 2 It may be a PLET or a PLEM. 3.1.22.
Source: API RP 17B, Recommended Practice for Flexible Pipe, Fourth Edition, July 2008. Global Standards