The OSM Terms of Reference state that:

All code contributions to OSM shall be made under the Apache License, Version 2.0 and the OSM Corporate or Individual Contributor License Agreements, signed as part of the process of joining OSM.

All outbound code will be made available under the Apache License, Version 2.0.

Also, all contributions of source code to OSM will include a signed-off-by statement and thereby the Developers Certificate of Origin (DCO).