What are uncirculated coins?

Excuse me, could you elaborate on the concept of "uncirculated coins"? I'm curious to understand what sets them apart from coins that are in circulation. Do they possess any unique characteristics or markings that differentiate them? Additionally, what is their significance in the realm of coin collecting and finance? Lastly, how does their rarity or scarcity impact their value in the market? I'm looking forward to your insights on this topic.