Original: Using the CC-BY-SA license and GFDL only Unless you explicitly specify otherwise, all contributions to Wikipedia are dual-licensed under the CC-BY-SA license and the GFDL; therefore, if you elect not to adopt additional licenses, no action is necessary.
Simplified: Using the GFDL only Unless you specifically say otherwise, all contributions to Wikipedia are licensed under the GFDL; therefore, if you elect not to adopt additional licenses, no action is necessary.