Wiktionary
potential well
n. (context physics English) The region surrounding a local minimum of potential energy.
Wikipedia
Potential well
A potential well is the region surrounding a local minimum of potential energy. Energy captured in a potential well is unable to convert to another type of energy ( kinetic energy in the case of a gravitational potential well) because it is captured in the local minimum of a potential well. Therefore, a body may not proceed to the global minimum of potential energy, as it would naturally tend to due to entropy.
Usage examples of "potential well".
He was in a deep potential well, he would tell visitors to Moscow in the metaphors of physics.