The Lumberyard Editor includes components of Qt, http://www.qt-project.org/, that are licensed under Version Version 3 of the GNU Lesser General Public License.  Source code for the Qt distributions used in Lumberyard can be found here:
    https://s3-us-west-2.amazonaws.com/ly-legal/LicenseConformance/Qt/Src.zip

Qt also includes a number of third party components that are licensed under other license terms; for details see https://doc.qt.io/qt-5/licenses-used-in-qt.html.