What is "portability" and to whom does it apply?

Bibliographic Details
Corporate Author:	United States. Employment Standards Administration. Wage and Hour Division
Format:	Government Document Book
Language:	English
Published:	Washington, DC : U.S. Dept. of Labor, Employment Standards Administration, Wage and Hour Division, 2008.
Series:	Fact sheet ; #62W
Subjects:	Foreign workers > Legal status, laws, etc. > United States.
Online Access:	https://purl.fdlp.gov/GPO/LPS101712

Available Online