ABSTRACT
The word “feedback” is by far one of the most used ones in modern cosmology where it is applied to a vast range of situations and astrophysical objects. However, for the same reason, its meaning in the context is often unclear or fuzzy. Hence a review on feedback should start from setting the definition of feedback on a solid basis. We have found quite useful to this aim to go back to the Oxford Dictionary from where we take the following definition.
