I would like to share a trilogy of articles since @Tef made a question "What does Unspent Transaction Output (UTXO) refers to?".
Although many users may not realize it, all bitcoin wallets need some level of maintenance to be properly managed. If you’re using a custodian, they take care of these things. However, when you hold your bitcoin in self-custody, no one is responsible for managing your wallet but you. To maintain your wallet properly, you’ll need to know what UTXOs are and how to manage them. - Tom Honzik
In this trilogy, the topic is explained very well.
The first article:
What is a bitcoin UTXO and why do they matter?
https://unchained.com/blog/what-is-a-utxo-bitcoin/
The second article:
More UTXOs, more problems: High fees, signing failures, and how to avoid
https://unchained.com/blog/too-many-bitcoin-utxos
The third article:
UTXOs, addresses, and CoinJoins: Preserving privacy in a bitcoin economy
https://unchained.com/blog/bitcoin-utxo-privacy
I hope these help you!