The Current Age
Kali-yuga is the fourth and final age (yuga) in the Hindu cosmic cycle of four yugas (Kṛta/Satya, Tretā, Dvāpara, Kali). In Kali, human lifespan, virtue, memory, and ritual capacity are all greatly diminished compared to prior ages. The yuga began at the departure of Kṛṣṇa from the earth (~3102 BCE by traditional reckoning) and lasts 432,000 years.
Dharma's Decline
In Kali-yuga, the full Vedic ritual regimen (krama) is held to be beyond the capacity of most human beings. This is precisely why the Āzhvārs appeared — to make the divine accessible through the Tamil Prabandham — and why prapatti and nāma-japa are emphasized as the appropriate dharma for the age: accessible, immediate, and fully efficacious.
Providence Within Kali
Paradoxically, Śrī Vaiṣṇava teachers regard Kali as uniquely graced: Bhagavān makes Himself more accessible in this age precisely because human limitations are greatest. The arcā (deity in the temple), the Divya Prabandham, and the Ācārya are Bhagavān's special provisions for Kali-yuga. Maṇavāḷa Māmunigaḷ is celebrated as Kali-yuga's preeminent Ācārya.