Compute Units
Plain English
Measure of computational work a transaction requires. Like CPU usage - complex transactions need more compute units. Solana has a limit per block. You can pay higher priority fees to get more compute units or faster processing. Simple transfers use very few.
Technical
Quantification of computational resources consumed by transaction execution. Each instruction has compute cost (BPF operations). Block limits: 48M CU total, 1.4M per writable account lock. Transactions specify max CU budget; excess returned. Priority fees (lamports per CU) enable transaction prioritization. Prevents state bloat and ensures fair resource allocation under congestion.