Reliability, scalability and maintainability.

Reliability

The system does what it is supposed to do at the expected level of performance, even in the presence of faults (human mistakes, software bugs, hardware failures).

Keywords: availability, durability, correctness, fault tolerance, graceful degradation.

Scalability

As load grows (traffic, data, users), the system can increase capacity predictably by adding resources (scale up/out) or by using elastic infrastructure—without disproportionate cost or latency growth.

Keywords: horizontal/vertical scaling, elasticity, throughput, latency.

Maintainability

The system is easy to understand, change, fix, and extend by different people over time, minimizing risk and effort.

Keywords: modular design, clear interfaces, tests, documentation, observability, automation.