There are Kavachas for several gods and goddess.
Is it a mantra? If yes, then which mantras falls into the category of Kavacha? If no, then what is the exact (scriptural) definition for Kavacha?
There are Kavachas for several gods and goddess.
Is it a mantra? If yes, then which mantras falls into the category of Kavacha? If no, then what is the exact (scriptural) definition for Kavacha?
A Kavacha is nothing but a Stotra having a peculiar feature.
Budha Kavacham (found in Brahma Vaivarta Purana) starts as follows:
Asya Budha kavacha stotra maha manthrasya
For the chant called Armour for Budha (mercury)
Kasyapa Rishi
The sage is Sage Kasyapa
Anushtup Chanda
Meter is Anushtup
Budho Devatha
God is Budha (mercury)
Budha Preethyarthe Jape Viniyoga
This chant is being done to please God Budha.
As you can see, it says Budha Kavacha Stotra. That means Kavacha is a Stotra.
Similarly, the Ketu Kavacham (found in Brahmanda Purana) starts as follows:
अस्य श्रीकेतुकवचस्तोत्रमंत्रस्य त्र्यंबक ऋषिः I अनुष्टप् छन्दः I केतुर्देवता I कं बीजं I नमः शक्तिः I केतुरिति कीलकम् I केतुप्रीत्यर्थं जपे विनियोगः II
Asya Sri Ketu-kavacha-stotra-mantrasya tryamabaka rishih, anushtup chandaha, ketur devata etc....
So, again this also shows that Kavacha is actually a Stotra.
The peculiar feature of such Stotras is that they ask various deities to protect the various limbs of the chanter.
In the Budha Kavacha, you will find that the various names of Budha (like Rohini Suto, Khageswara etc. ) are requested to protect different body parts of the aspirant.
Granam gandha priya pathu, jihwam vidhyapriyo mama,
Kantam pathu vidho, puthro bhujow pusthaka bhooshana., 3Let my sense of smell be protected he who likes scents,
Let my toungue be protected by he who likes knowledge,
Let my neck be protected by the knowledgable one,
Let my arms be protected by he who is decorated by books.
Here Gandhapriya, Vidyapriya, Vidhuputra etc. are various names of Budha, which are requested to protect certain limbs of one who is reading the Kavacha.
Similarly is composed the Ketu Kavacham or any other Kavacha-Stotra in general.
They act on us like how a physical armor will act by protecting us.
Is it a mantra?
Yes. it is a Mantra too.
As you can see from the given examples.
Budhakavachamahamantrasya and Ketukavachastotramantrasya --- so a Kavacha is a Stotra and at the same time it is a Mantra as well.
Since, a Mantra that has more than 20 syllables is called a Mala Mantra, therefore any Kavacha will be technically a Mala Mantra.
EDIT:
An example of a Stotra that is a Mantra but not a Kavacha, is the Devi Khadgamala Stotram.
It starts with the Viniyoga:
Om Asya Sri Suddha Sakti málá mahá mantrasya
Upasthendriya adhisthayi Varunaditya Rishih
Devi Gayatri Chandah
Satvika Kakára bhattaraka pithasthita
Sri mat Kámesveranka nilaya
Sri mat Kámesvari devatá
Aim Bijam, Klim Saktihi, Souh kilakam
Sri Devi prityarthe Khadga siddthyarthe jape viniyogah
To the pure garland of prayers to Goddess Shakthi ,
Which should be worshipped by all sense organs,
The Sage is the rising Sun,
The meter is Gayathri and the goddess presiding is Goddess Kameswari ,
Who exists in the peaceful Kameswara who is sitting on the seat of Kakara Bhattaraka,
The root is Im , the power is kleem , Sopu is the pivot ,
And is being chanted to please the Goddess and getting her sword.
It is of course a Stotra, as the name itself suggests, but at the same time it is a Mantra (a Mala Mantra to be precise since it has more than 20 syllables) as well.
But it is NOT a Kavacha since it does not have the aforementioned feature of a Kavacha.
So, in this way you have to differentiate between a Stotra and a Kavacha.