What kinds of things can an honorary doctorate be awarded for?

People who have earned honorary degrees include actors and musicians such as Leonardo DiCaprio and Justin Timberlake; scientific pioneers such as Albert Einstein; politicians such as Hillary Clinton; writers such as Shakespeare; athletes such as Michael Jordan and Serena Williams; educators such as James Baldwin; scientists such as Stephen Hawking; doctors like Thomas Alva Edison; inventors like Thomas Edison; philosophers like Jane Austen; religious leaders such as Pope John Paul II and Mother Teresa; philanthropists like Bill Gates.