From AMS Glossary
A current in which the dominant balance is between the inertial and the Coriolis terms in the equation of motion, causing streamlines to be curved to the right (left) in the Northern (Southern) Hemisphere.
If we think of the streamlines in an inertial current as being locally circular with radius of curvature R, and speed V along the streamlines, the balance of forces in the radial direction is
where f is the Coriolis parameter. Thus, the radius of curvature is V/f, which is about 10 km for a 1 m s-1 current.