[ Thanks to Amy
Bennett for this link. ]
“When a software developer creates a particular piece of code
and wants to contribute it to a larger project, there needs to be
some sort of agreement (formal or informal) as to what kind of
license the contributed bit of code (the “incoming” license) will
have in relation to the license of the larger project (the
“outgoing” license). Ideally, you want the incoming license and the
outgoing license to match up, because you wouldn’t want, say, the
incoming license be GPL and the outgoing license be a BSD
license.“When the project is manage by a commercial company, things get
a little more complicated. These companies typically want to make
really sure their investment in the software is protected, so what
they usually do is formally ask contributors to sign a Contributor
License Agreement (CLA), which usually require contributors to not
only certify the code they’re turning in is clean, but also grant
the project full rights to control the license of the contributed
code within the project indefinitely.”