In fluid mechanics, the Reynolds number is a dimensionless quantity that helps predict fluid flow patterns in different situations by measuring the ratio between inertial and viscous forces. Wikipedia

A dimensionless quantity in fluid mechanics used to help predict flow patterns Wikipedia Disambiguation

Dimensionless quantity that is used to help predict similar flow patterns in different fluid flow situations Wikidata

A dimensionless parameter that determines the behavior of viscous flow patterns. In pipe flow a value less than about 2,000 (known as the critical Reynolds number) produces laminar flow, one above about 3,000 produces turbulent flow (intermediate values produce unpredictable behavior). Wiktionary

Dimensionless parameter of flow. Wiktionary (translation)