Great question! UTXOs, or Unspent Transaction Outputs, are basically the "change" left over when you spend Bitcoin.

Imagine this: You've got a 10 BTC input but want to send someone 1 BTC. What happens? Well, you'd actually send the whole 10 BTC - but then get back 9 BTC as change in form of a new UTXO.

So your balance is just the sum of all UTXOs controlled by your private keys. It's a bit like counting all the loose change in your pocket to figure out how much money you've got!

Hope that makes sense! Keep those Qs coming.