The answer is both. The official name of the country in which Amsterdam is located is the Kingdom of the Netherlands. Within the Netherlands there are 12 administrative provinces, two of which contain the name Holland. Amsterdam lies in Noord-Holland, or North Holland. Zuid-Holland, or South Holland, lies just south (imagine that) and includes the Netherlands' official seat of government, the city of Den Haag.
Confused about the capital of the Netherlands? Find out if it's Amsterdam or Den Haag (The Hague).