What Is Āgama?
Āgama ('that which has come [from above]') refers to a class of revealed scripture distinct from but complementary to the Vedas. Āgamas address practical theology — the forms of God, modes of worship, temple construction, icon consecration, yoga, and philosophical instruction — in ways that the Vedas address only obliquely.
Pañcarātra Āgamas
For Śrī Vaiṣṇavas, the most important Āgamas are the Pañcarātra texts (including Jayākhya, Sātvata, Pauṣkara Saṃhitā, and others). These describe: the Vyūha system (divine emanations), the five modes of Bhagavān's presence (para, vyūha, vibhava, arcā, antaryāmin), Vaikuṇṭha cosmology, and the protocols of āgamika temple worship.
Āgamika Authority
Āḷavandār's Āgama-prāmāṇya and Rāmānuja's Śrī Bhāṣya (Pañcarātra section) establish that the Pañcarātra Āgamas are valid śabda-pramāṇa — not in conflict with the Vedas but supplementing and specifying what the Vedas indicate more generally. This defense of Āgamic authority was crucial for grounding temple worship theologically.