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Technical Vocabularynoun · /ˈrʌn.taɪm/

runtime

In simple English

In software development, runtime refers to two closely related concepts. First, it describes the time period when a program actually executes on a machine, as opposed to compile time when the code is being prepared or parsed. Second, it refers to the runtime environment—the software infrastructure needed to run applications, such as the Java Runtime Environment (JRE) or Python interpreter. In daily tech work, engineers constantly discuss runtime behavior, runtime errors, and runtime performance. A runtime error is one that happens while the program is running, not during compilation. Teams optimize runtime performance to ensure applications respond quickly. Understanding the difference between compile-time and runtime issues is critical for debugging and development.

What is runtime and when do runtime errors occur in programming?

At a glanceCEFR B2
Commonness5/5
Versatility4/5
FormalityCasualFormalNeutral
Spoken ↔ WrittenSpokenWrittenBoth
Directness ↔ DiplomaticDirectDiplomaticDirect
RegionUS and UK
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Say it like this

✓This bug only appears at runtime
✓We need to optimize runtime performance
✓The runtime environment is not configured correctly
✓Runtime errors are harder to catch than compile errors

Real examples

in a standup

"We discovered a runtime error in the payment module, so we are pushing the release back by one day."

in a code review

"This code might cause runtime issues if the user passes a null value."

in a team meeting

"We need to improve runtime performance on mobile devices; the app is too slow."

in a technical discussion

"The runtime memory usage increased significantly after we added the new logging feature."

Don't say this

Handle with care. Do not confuse runtime (the period when code runs) with compile time (when code is converted to machine language). Also avoid using it as a verb; say 'execute at runtime' not 'runtime the code'.

✕We need to runtime the tests before deployment.
✓We need to run the tests at runtime before deployment.— Runtime is a noun, not a verb. Use 'run' or 'execute' instead.
✕The runtime error occurred during compile time.
✓The runtime error occurred during execution.— Runtime errors occur while the program is running, not during compilation.
✕Our application has a good runtime.
✓Our application has good runtime performance.— Be specific about what aspect of runtime you mean—performance, stability, etc.

Other forms

noun

runtime

"The runtime of this service is typically under 100 milliseconds."

noun (modifier)

runtime

"We need to check the runtime environment before starting."

Often used with

at runtimedescribes when something happens during program execution
runtime erroran error that occurs while the program is running
runtime environmentthe software needed to execute a program
runtime performancehow fast and efficiently a program runs
runtime behaviorhow a program acts when it is executing
reduce runtimeto make a program execute faster

Similar words

execution timemore formal; refers specifically to how long the program runs
executionshorter and more general; refers to the act of running
runtime environmentspecifically refers to the software infrastructure, not the time period

Opposites

compile timedesign timedevelopment time

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Practice

Try it

4 quick exercises

Pick the most natural phrasing

1. Your code has a bug that only happens when the application is running. How do you describe it?

Complete the sentence

2. This feature works fine during testing, but it crashes _______ in production.

Spot the mistake

3. Which sentence uses 'runtime' incorrectly?

Rewrite naturally

4. Rewrite this in natural tech English: 'The program is running and we found an error that happens while it is executing.' Use the word 'runtime'.

Questions

Quick poll

Have you said "runtime" in a standup this week?

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