Full Idea
An object satisfies an open sentence if and only if it possesses the property expressed by the predicate of the open sentence.
Gist of Idea
An open sentence is satisfied if the object possess that property
Source
Richard L. Kirkham (Theories of Truth: a Critical Introduction [1992], 5.4)
Book Reference
Kirkham,Richard L.: 'Theories of Truth: a Critical Introduction' [MIT 1995], p.153
A Reaction
This applies to atomic sentence, of the form Fx or Fa (that is, some variable is F, or some object is F). So strictly, only the world can decide whether some open sentence is satisfied. And it all depends on things called 'properties'.