(This is taken from Rhino's COPYING file.)

Rhino is free software; see the copyright notice in each file for the terms under which it may be redistributed and/or modified.

As Rhino is composed mostly of header files & libraries, most files are licensed under the terms of the LGPL; in general the standalone commands and test programs are licensed under the terms of the GPL, except for the Java test programs, which are LGPL.