This is an armour hymn (kavacha stotra) of lord Hanuman. It is called a kavacha stotra because it is made of a set of prayers, where we request lord hanuman to protect the directions and different parts of the body, by invoking him through different names which indicates different qualities or pastimes of hanuman.
This armour of hanuman that was first sung by lord rama, a protective hymn of hanuman which blesses us with health, wealth, victory etc. this is attributed to the brahmanda purana but it is found in mantra maharnava, an authentic work that deals with mantras of various deities.
A variation of this kavach is also found in the narada mahapurana, where this kavacha is a part of a longer stotra.
In this book I will be using the recitation that is recorded in the text mantra maharnava.