Synchronous phenomena are central to many fields, including technology, finance, molecular biology, physics, music and psychology (see Supplementary Information for references). Yet conceptual inconsistencies are thwarting the upsurge of interest in this ubiquitous topic, which a shared definition of synchrony could address.

Synchrony is often taken to mean loose coordination patterns among processes, individuals or populations — tidal rhythms and animals' mating behaviours are examples. In this guise, synchrony has teleological and mechanistic connotations. Alternatively, synchrony can refer to the precise coincidence of events in time, such as two photons reaching a sensor or musicians playing in unison.

Conflating different meanings generates confusion and misinterpretation. It is time to engage in an interdisciplinary debate and converge on common definitions. We might, for instance, adopt the most restrictive definition of synchrony — already used in mathematics and physics — and appropriately qualify looser forms of co-occurrence. This would endow the life sciences and social sciences with the quantitative tools that mathematics has been refining for decades.