Just noticed this in data.census.gov.
The Census Bureau does not release ACS data at the ZIP Code level, but instead for ZIP Code Tabulation Areas (ZCTAs), which are generalized representations of U.S. Postal Service ZIP Code service areas…
It may be a little bit out of date, but I wrote this blog post about the difference a few years ago: www.policymap.com/.../what-are-zip-code-tabulation-areas
The Census Bureau does not release ACS data at the ZIP Code level, but instead for ZIP Code Tabulation Areas (ZCTAs), which are generalized representations of U.S. Postal Service ZIP Code service areas. The Census Bureau has a short video that explains how ZCTAs differ from ZIP Codes. However, it looks like 5-Digit Zip Codes are listed as a geography in data.census.gov because they are available in a limited set of Census Bureau data sets, such as County Business Patterns.