Can I have a clarification on this please ? 

Allowed

• General-purpose code, i.e. character controller, project template, menu functionality, AI library, etc.
• Freely available assets including open general-purpose source code.

So assets include art assets I assumed. Can one use art assets from unity store ? I am running solo and not an artist, so I usually rely art assets from the store that I put together to get a better looking prototype quickly, is that cool ?

Yes, assets include audio, visuals, code, shaders, text - anything that goes into a game. As long as it's freely available (meaning anyone could use it) then you can use it in the jam. 

But note that we limit any related score for Judges Choice to 4/5, so you can only score 5/5 for Graphics/Animation if the visuals are original - and you will be required to list any assets which are not your own, which may also affect your Developers Choice score.