Reliability
Reliability is the degree to which a software system performs its required functions consistently for a specified period under specified conditions.
“The degree to which a component or system performs specified functions under specified conditions for a specified period of time.”
(Definition reproduced from the ISTQB Glossary. Copyright belongs to ISTQB.)
View the complete ISTQB GlossaryWhat is Reliability?
Reliable software operates without unexpected failures and continues providing correct results throughout normal operation.
Consistent operation: Functions perform correctly over time.
Failure resistance: Reliable systems minimize unexpected interruptions.
Quality characteristic: Defined in ISO/IEC 25010.
Real World Example
A national travel service is preparing for a public holiday sale where thousands of users may search, reserve, and pay for tickets at the same time.
A feature that works for one tester may fail under traffic, resource pressure, or infrastructure disruption. Reliability helps the team focus on behavior under operational conditions.
The tester defines realistic traffic, failure, and recovery situations, then watches response time, errors, data consistency, and whether users can continue critical actions.
The release decision improves because Reliability gives stakeholders evidence about service behavior when demand or disruption is no longer theoretical.
Practice Questions
Question 1
Which statement BEST describes Reliability in the context of ISTQB terminology?
Question 2
A tester needs to explain Reliability to a non‑technical stakeholder. Which approach is MOST appropriate?
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