Why am I reading less than nominal voltage on my receptacle?
you have dropped a neutral.
the white wire is gone.
also called a loose neutral.
check all receptacles on the circuit.
if its only the one. turn off power and check the wiring is tight.
if its tight replace
if its loose tighten. (you should replace anyways. loose connection could have caused damage)
if its all of them and you notice that lights are a little dim in that area of the house. start at the breaker panel and work your way through he circuit checking for loose connections.
a 3light plug checker may read hot-ground reversed on an open neutral not open neutral.
the good news is that your nice and grounded.