Explain the CAP theorem in distributed systems.

CAP says a distributed system can guarantee at most two of: - **Consistency (C):** every read sees the latest write. - **Availability (A):** every request gets a non-error response. - **Partition tolerance (P):** the system works even when nodes can’t communicate. Because partitions happen in real systems, you usually choose **CP** or **AP** behavior during failures. **Interview tip:** Give examples: CP-like systems favor correctness; AP-like systems favor uptime with eventual consistency.