Acceleration of maturity

What does Acceleration of maturity mean in American Law?

The definition of Acceleration of maturity in the law of the United States, as defined by the lexicographer Arthur Leff in his legal dictionary is:

Essentially the same meaning of “acceleration” as in an acceleration clause, except that the acceleration of obligation is pursuant to the payee’s discretion, the exercise of which need not be made dependant upon any default by the obligor.