'Spinning' = pedalling with a higher cadence than normal. 80rpm+. Trikes tend to prefer riding with a high cadence than normal. Less strain on the knees and less power required for a given speed. Recumbents in general allow you to apply huge amounts of power to the pedals because you can push your back into the seat. On a DF you are limited by your own weight in how much power you can put into the pedals.
'Mashing' = riding in too high a gear. Mashing hurts the knees. Even on a DF bike spinning is preferred to mashing.
I can sprint on my Wisper to 22mph for a short period with alarming acceleration (so my friend once said). I'm already at 80rpm and can easily put power in quickly just by running up to about 110rpm. Shift to next cog up to maintain speed but the legs tire too quick (for me at least).
I find I can accelerate quickly on my trike using the same technique. Cruise in 7th at 15mph. Nip up to 8th with a wind behind me for 18mph. Trikey spins out just after 18mph. By that I mean I can't pedal any faster to get more speed.
I've probably not explained it very well.
Best regards.
Vikki.