What is so "potential" about action potentials?
There are other meanings of "potential" than the regular meaning "having or showing the capacity to become or develop into something in the future" (source: Google Translate).

In case of "resting potential" it refers to the voltage difference across the cellular membrane. Every cell maintains a voltage difference across the membrane (see a related question here: https://biology.stackexchange.com/questions/17840/resting-and-action-membrane-potential). The voltage difference is used for various purposes, including the transport of nutrients and ions, and it is crucial for action potentials to occur.  

In case of "action potential" it refers to a series of successive changes in the voltage difference across the membrane, which occurs when an excitable cell is triggered (see a related question here: https://biology.stackexchange.com/questions/91/how-do-the-brain-and-nerves-create-electrical-pulses/110#110).