Background information is general information about a writer, their works, and their social/historical context that can help you better understand specific pieces of literature.
The sources below are some library-provided options for finding background information. Some of them may also contain other types of information, but we are highlighting the background information here.
If you encounter an unfamiliar word when reading a piece of literature, the Oxford English Dictionary is an excellent resources. This is especially useful for words that are no longer in common use, and for understanding the history and origins - the etymology - of such words.