What does concurrency mean?
Concurrency refers to the condition of two or more events, tasks, or processes taking place during the same period of time. Although the idea is ancient — historians speak of the concurrency of political crises, for example — the word has become most prominent as a central concept in computer science. There, concurrency describes a system's capacity to run many tasks with overlapping execution: a web server serving thousands of visitors simultaneously, or an operating system juggling dozens of programs at once. Concurrency is distinct from parallelism, which strictly means executing tasks at the same instant on separate processors; concurrent tasks may simply interleave. Managing concurrency safely, so that simultaneous operations do not corrupt shared data, is among the most challenging problems in software engineering, giving rise to techniques such as locks, atomic operations, and concurrency control. Outside computing, the word carries a formal, academic tone and often appears in discussions of coinciding events or overlapping responsibilities.
nounThe fact or condition of two or more events, activities, or processes happening or existing at the same time; in computing, the ability of a system to execute multiple tasks during overlapping time periods.
- In computing: the ability of a program or system to manage multiple tasks whose execution overlaps in time.
- The general fact of two or more things happening or existing at the same time.
"The database was designed to handle high concurrency without locking records unnecessarily."
"The server can handle thousands of concurrent connections thanks to careful attention to concurrency."
"The concurrency of two major festivals made hotel rooms nearly impossible to find that weekend."
Rare; used mostly in technical writing to count individual simultaneous sessions or transactions (e.g. billing by number of concurrent users).
"The pricing plan allows up to five concurrencies per account."
Every time you scroll a feed while music streams in the background, you're watching concurrency at work — and it's one of the hardest problems in computer science.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of concurrency
Concurrency derives from the Latin verb 'concurrere', meaning 'to run together' or 'to coincide', formed from 'com-' ('together') and 'currere' ('to run'). English adopted the noun via the adjective 'concurrent' and the older noun 'concurrence', which entered the language around the early 17th century from post-classical Latin 'concurrentia' and Old French. Its sibling words share the running root: 'occur', 'recur', and 'incur' all trace back to Latin verbs built on 'currere', while 'course' and 'current' come through French from the same stem.
Related word forms
How concurrency is actually used
Predominantly technical register — most common in software engineering and systems literature, where it is a core term of art. In general usage it sounds somewhat formal or academic; everyday speech more often uses phrases like 'at the same time'. The plural 'concurrency' is rarely used; when multiple instances are meant, writers typically say 'levels of concurrency' or keep it uncounted.
Easily confused with concurrency
Concurrence usually means agreement or approval (as in 'with your concurrence'), while concurrency refers to simultaneous occurrence, especially of processes or events.