Cubase media bay items

Ive recently started using loops from the media bay, one type has me a bit confused. It has a sort of timer or loop icon (see attachment). When I import this into the project I get a midi track with a sample (or instrument ?) I cant really tell. What type of media is this ?

Exactly that, MIDI loops.

so where does the actual sound come from, is it a sampler track ?

No, when you export a MIDI part as a MIDI loop it saves the parameters for the VST instrument loaded on the track. So when you play it in the media bay, it uses the that VST instrument to play the MIDI part. The factory content MIDI loops included with Cubase use Groove Agent and Halion, I think.

To be honest, I have no idea what it uses as a default VST instrument for the preview if you don’t have the instrument the loop was made with (or if it previews the file at all).