A copyright is when something has originality and gets protected so others can not steal its rights. Some work that can be copyrighted is about anything like plays, music, literature, sound recordings and more. Somethings that can’t be copyrighted is ideas, facts, titles and a few other exceptions. The length of a copyright varies on when the work was created and the country it was registered. It usually is the span of the creators lifetime plus 70 years after the death. To claim a copyright you have to file one with the US Copyright Office. One example of a copyrighted song is Happy Birthday. This has been a legal battle for last two years due to not being able to use the song because of copyright. The battle showed legal evidence that the 1972 version of “Happy Birthday to you” was without a copyright. So the song has technically been in the public domain no later than 1922.
So sing Happy Birthday with a copyright fine! Yay!