Step 1: Understanding the Concept:
To correctly classify a Purana, one must refer to the traditional lists of the 18 Mahapuranas and the 18 Upapuranas. While 'Maheshvara' is a name of Lord Shiva, and there is a Mahapurana called the 'Shiva Purana' (or Vayu Purana in some lists), the Maheshvara Purana specifically is a different text recognized as an auxiliary work.
Step 2: Detailed Explanation:
The Maheshvara Purana is classified under the Upapurana-vidhayam (Minor Purana category). In the traditional list of eighteen Upapuranas (as found in texts like the Kurma Purana or Padma Purana), the Maheshvara Purana is explicitly mentioned.
It is a Shaiva text that focuses on the glorification of Shiva (Maheshvara), details about Shaiva rituals, the significance of the Linga, and specific myths related to the Maheshvara form of the deity. Since the 18 Mahapuranas are fixed (Brahma, Padma, Vishnu, Shiva/Vayu, Bhagavata, Narada, Markandeya, Agni, Bhavishya, Brahmavaivarta, Varaha, Skanda, Vamana, Kurma, Matsya, Garuda, Brahmanda), any other Purana like the Maheshvara falls into the secondary category of Upapuranas.
The other categories mentioned:
- Aupapurana (Option C) and Upopapurana (Option D) are much later classifications used by some scholars to categorize even smaller, regional, or highly specific texts (often called 'Sthala Puranas'), but they are not the standard canonical divisions. The term Upapurana is the broad, recognized canonical term for the second-tier Puranas.
Step 4: Final Answer:
It is classified in the Upapurana category.