A latent ambiguity is one that only arises when applied to the facts. E.g., it says to give it to someone but there are two people by that name.
Latent ambiguities can be between exact fits or partial fits.
Equivocation is a latent ambiguity where two or more people exactly fit the description in the will.
Personal usage is an exception to the plain meaning rule. It allows extrinsic evidence to show the true meaning of terms the testator habitually used in an idiosyncratic manner.
E.g., if you have a friend named Jeanilee, but you exclusively and oddly call her "Vicky" in your folly, extrinsic evidence would be admitted to resolve who Vicky is.
Extrinsic evidence will be admitted to resolve latent ambiguities under both common law and modern law.
Latent ambiguities can also be partial fits. If no one person fits the description, but multiple partially fit it, extrinsic evidence will also be allowed to resolve the ambiguity.