One of the names of Śiva-Mahādeva (Shiva-Mahadeva) in Aṣtottara Sahasranāma (Ashtottara Sahasranama) of Śiva. The annotator Nīlakaṇṭha (Nilakantha) has explained the name as such—
pravṛttaṃ śāstramanusaran sādhaka ityarthaḥ.
The word adhyātma (adhyatma) signifies to claim one’s ātmā (atma, roughly translated as soul or spirit). To put it simply, it means to be able to have one’s sensual and material tendencies within one’s own control. According to Upaniṣadas (Upanishadas), God Śiva is a form of paramātmā (paramatma, roughly translated as the Supreme Spirit). He has complete command over his senses, he is above and beyond corporeal desires. But when he is referred to as Adhyātmānugata (Adhyatmanugata), what is highlighted are his restraint over his senses, and his form as a yogī (yogi) and ascetic. He is Yogīśvara (Yogishwara, or the god of ascetics), the supreme among ascetics. Hence his appellation as such.