MMP (Maximal Minute Power) and FTP (Functional Threshold Power) are both maximal fitness tests that can be used to measure performance and prescribe training zones. The standard test for FTP is riding at a constant power for an hour, many people shorten this and complete a 20 minute test and take of a percentage of the power score achieved (e.g. 95%). Whereas the standard test for MMP would be to complete a ramp test and record the final full minute completed.
British Cycling developed the 3 minute test, in which Wattbike has adopted to measure MMP. The 3 minute test gives a good estimation of maximal aerobic power that you would achieve at the end of a ramp test.