A Unix timestamp is the number of seconds since January 1, 1970 UTC. Timestamps are used in blocks to ensure that blocks accumulate in a chronological order.
A UTXO is a discrete piece of bitcoin. Bitcoin does not use accounts and balances. Instead, individual pieces of bitcoin are owned by individuals, analogous to physical coins or cash.
A User-Activated Soft Fork is an update or change to the Bitcoin network’s protocol initiated by users (nodes), who integrate new code into their Bitcoin nodes.
Universal Time Coordinated (UTC) is a specific timezone and is used as a standard for international timekeeping. UTC used to be known as Greenwich Mean Time or GMT.
The UTXO set is the comprehensive set of all UTXOs existing at a given point in time. The sum of all UTXOs will yield the precise current supply of Bitcoin.