Can you tell me what is a pen name?

A pen name is a name an author publishes a book under. It isn't their real name, it's only the name they go by when writing books.

Many female authors used male names to publish their books in time periods such as 1700s or 1800s, when women weren't thought of as smart and they didn't have rights. The male names were their pen names, used so that people would respect them.

Examples in modern day (pen name --> real name):
J.K. Rowling (Harry Potter) --> Joanne Kathleen Rowling
Lemony Snicket (Series of Unfortunate Events) --> Daniel Handler

A 'pen name' is the name a writer uses on the things he writes. It doesn't have to be
his real name.

The French phrase is "nom de plume" . . . "name of the pen".

An example:

In the 19th Century (the 18 hundreds), there were several great French novels
that were written by George Sand, and they became very popular.

Except that George Sand was really a lady named Armandine Aurore Lucille Dupin,
who was married and had two children.