The Netherlands is a country in northwest Europe comprising twelve provinces. Holland is the western part of the Netherlands, consisting of the provinces of North Holland and South Holland. Holland contains the largest cities in the Netherlands—Amsterdam, The Hague, and Rotterdam. Holland can informally refer to the whole of the Netherlands; this is an example of synecdoche, akin to using England to mean the United Kingdom.
The word Dutch refers to the people and language of the Netherlands, or to anything from or related to the Netherlands.