What does a proxy mean in Python?

http://flask.pocoo.org/docs/1.0/reqcontext/#notes-on-proxies says

Some of the objects provided by Flask are proxies to other objects. The proxies are accessed in the same way for each worker thread, but point to the unique object bound to each worker behind the scenes as described on this page.

Is "proxy" a concept in Python language or somewhere else (such as design patterns)?

What is its definition?

Thanks.