Local and Non-Local Dependencies
A local dependency is a dependency between two words expressed within the same syntactic rule.
A non-local dependency is an instance in which two words can be syntactically dependent even though they occur far apart in a sentence (e.g., subject-verb agreement; long-distance dependencies such as wh-extraction).
Non-local phenomena are a challenge for certain statistical NLP approaches (e.g., n-grams) that model local dependencies.