What does underrun mean?
Underrun is chiefly a computing term for a failure to keep pace. As a verb, a system or program underruns when it cannot manage its workload or deliver data at the rate an operation requires; during real-time playback, for example, the condition may leave a buffer empty. As a noun, an underrun is the condition itself or a particular occurrence of it. The word therefore describes both an ongoing process and a discrete fault that can interrupt playback, communication, or another timed operation. It is not normally used as a general synonym for “fall behind,” where it would sound conspicuously technical. Its importance lies in timing: an underrun often appears when a design is otherwise correct but its workload assumptions fail under real conditions. Related terms such as overrun express the opposite capacity problem. Familiar expressions including input underrun and buffer underrun make the intended context clearer. Although formed from ordinary words, underrun is useful because it names a specific failure mode rather than merely saying that something was slow.
A condition or instance in which a computer or other system cannot keep pace with its workload or deliver data at the required rate, often causing a buffer to empty.
"A brief playback underrun caused the video to freeze for a fraction of a second."
The noun may denote the general condition or a countable individual occurrence.
To fail to keep pace with a processing workload or to deliver data at the rate required by an operation.
"The audio stream underruns when the player cannot supply samples to the speaker quickly enough."
Chiefly used in computing, telecommunications, and real-time media.
The plural is underruns and is used for individual occurrences of the condition.
"Several underruns made the live stream unstable."
Underrun captures a digital paradox: a system can have enough data overall yet still run dry at the exact moment it needs the next piece.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does underrun come from?
Underrun is an English compound formed from under and run. Its now-familiar technical sense developed with the use of computers to process continuous workloads and streams of data, especially in real-time systems. The same compound-building pattern appears in words such as overrun and outrun, which relate semantically to going beyond, across, or ahead of another limit.
Related word forms
How underrun is actually used
This is specialized technical vocabulary rather than ordinary general English. In media and systems contexts, it normally describes a timing or capacity failure rather than physically passing beneath something.
Easily confused with underrun
An overrun occurs when a system receives or processes more data than it can handle, whereas an underrun occurs when it cannot maintain the required rate or when a buffer empties.