If you click the "?" icon in Muse Monitor, you can read about this in the in app help, or you can view the same information online at MuseMonitor.com by clicking on Technical Manual in the top menu.
Alpha, Beta, Gamma, Delta and Theta are brainwaves, the values for which are the Power Spectral Density for a specific frequency range. So for example, with Delta, that range is 1Hz to 4Hz. The higher the Delta number, the more brainwave activity you have between 1Hz and 4Hz at that point in time.
TP9, AF7, AF8 and TP10 are the four muse sensor locations. The naming comes from the standard 10-20 EEG system: