What are the key governor limits developers must know?

Key synchronous governor limits:

1. SOQL queries: 100 per transaction.
2. SOQL rows returned: 50,000.
3. DML statements: 150.
4. DML rows: 10,000.
5. Heap size: 6 MB.
6. CPU time: 10,000 ms.
7. Callouts: 100 (max 120 seconds per callout).
8. @future calls: 50 per transaction. Asynchronous limits are higher (e.g., Heap 12 MB, 200 SOQL). Limits reset per transaction, not per user or org. Use Limits.getQueries() and similar Limits class methods to programmatically check usage. Design patterns to avoid limits: bulkification, SOQL for loops for large data sets, asynchronous processing (Batch, Queueable).