The properties file
is a collection of key,value pairs of the form key=value1,value2,...
Property files may reference other properties. For example:
prop1=a,b,c,d,e
prop2=${prop1},f,g,h
The properties file can be placed anywhere on the file-system that Jenkins can access.
This property file has different meaning for multi-level select -- see the parameter type help for more info.