What is "upper nyack"

Population (2000): 1863
Housing Units (2000): 732
Land area (2000): 1.324319 sq. miles (3.429971 sq. km)
Water area (2000): 2.903623 sq. miles (7.520350 sq. km)
Total area (2000): 4.227942 sq. miles (10.950321 sq. km)
FIPS code: 76386
Located within: New York (NY), FIPS 36
Location: 41.107763 N, 73.922529 W
ZIP Codes (1990):
Note: some ZIP codes may be omitted esp. for suburbs.
Headwords: