Let's look at the Oxford Living Dictionaries definition to start with:
amp (noun)
short for amplifier
(verb [with object]) often amp something up
play (music) through electric amplification
Their willingness to amp up traditional songs virtually began the folk-rock genre.
(as adjective) amped or amped up (North American, informal)
full of nervous energy
Third-ranked Ohio State visits an amped-up Madison
Based on this, for amp to denote some classification of music, I see two possibilities:
First, amped could mean amplified, i.e. not acoustic - the normal definition of the verb given above. I think this is unlikely, for a number of reasons - it seems an odd classification for a website to make based on a playlist, and perhaps a difficult one to make too, but, mainly because it isn't a 'mood'.
Plugged-in or electric or amped in that sense doesn't fit with the other 'moods' we can see in your screenshot: danceable, chill or happy.
Second, amped could mean excited, pumped, hyped - the adjectival definition given above - full of nervous energy.
This definition fits better in context with danceable, chill and happy and is much more likely the intended meaning. (For what it's worth, I don't think these 'moods' seem to be a great classification system myself and I also think amped was quite a poor choice of name, given its ambiguity.)