The Atman is a philosophical term used within Jainism

Jainism

Jainism is an Indian religion that prescribes a path of non-violence towards all living beings. Its philosophy and practice emphasize the necessity of self-effort to move the soul towards divine consciousness and liberation. Any soul that has conquered its own inner enemies and achieved the state...

 to identify the soul. It is one's true self (hence generally translated into English as 'Self') beyond identification with the phenomenal reality of worldly existence. As per the Jain cosmology

Jain cosmology

Jain cosmology is the description of the shape and functioning of the physical and metaphysical Universe and its constituents according to Jainism, which includes the canonical Jain texts, commentaries and the writings of the Jain philosopher-monks...

, atman or soul is also the principle of sentience

Sentience

Sentience is the ability to feel, perceive or be conscious, or to have subjective experiences. Eighteenth century philosophers used the concept to distinguish the ability to think from the ability to feel . In modern western philosophy, sentience is the ability to have sensations or experiences...

 and is one of the tattvas

Tattva (Jainism)

Jain metaphysics is based on seven truths or fundamental principles also known as tattva or navatattva, which are an attempt to explain the nature and solution to the human predicament. The first two are the two ontological categories of the soul jīva and the non-soul ajīva, namely the axiom that...

or one of the fundamental substances forming part of the universe.