The local coefficient of risk aversion for a utility function u(x) where x is wealth...

https://riskprep.com/images/stories/questions/102.06.a.png  is the coefficient of risk aversion at x. Its inverse, ie https://riskprep.com/images/stories/questions/102.06.b.png , is called the coefficient of risk tolerance.

Risk aversion or risk tolerance is indicated in a utility function by its curvature. A concave utility function indicates risk aversion and a convex function indicates risk tolerance. The curvature is measured as a ratio of the second derivative to the first derivative of a function. A negative second derivative implies concavity. The expression is the coefficient of risk aversion, and its inverse, which is in the same units as wealth, is called the coefficient of risk tolerance.