For complete license details review LICENSE.txt.
GeoServer is free software and is licensed under the GNU General Public License:
GeoServer, open geospatial information server Copyright (C) 2014-2016 Open Source Geospatial Foundation. Copyright (C) 2001-2014 OpenPlans This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version (collectively, "GPL"). As an exception to the terms of the GPL, you may copy, modify, propagate, and distribute a work formed by combining GeoServer with the Eclipse Libraries, or a work derivative of such a combination, even if such copying, modification, propagation, or distribution would otherwise violate the terms of the GPL. Nothing in this exception exempts you from complying with the GPL in all respects for all of the code used other than the Eclipse Libraries. You may include this exception and its grant of permissions when you distribute GeoServer. Inclusion of this notice with such a distribution constitutes a grant of such permissions. If you do not wish to grant these permissions, remove this paragraph from your distribution. "GeoServer" means the GeoServer software licensed under version 2 or any later version of the GPL, or a work based on such software and licensed under the GPL. "Eclipse Libraries" means Eclipse Modeling Framework Project and XML Schema Definition software distributed by the Eclipse Foundation and licensed under the Eclipse Public License Version 1.0 ("EPL"), or a work based on such software and licensed under the EPL. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Suite 500, Boston, MA 02110-1335 USA
This product includes software developed by the Eclipse Software Foundation under the Eclipse Public License.