1. A narrow valley, especially one in a mountainous region. This is the most common meaning. It often refers to a valley with a stream or river running through it. Examples include:
* Glencoe in Scotland
* Glen Canyon National Recreation Area in the US
2. A part of the body, especially a bend in the shoulder. This is a less common usage, often used in the context of medicine or anatomy.
So, the meaning of "glen" depends on the context in which you encounter it.