Kali Yuga (Devanāgarī: कलियुग [kəli juɡə], lit. "age of [the demon] Kali", or "age of vice") is the last of the four stages the world goes through as part of the cycle of yugas described in the Indian scriptures. The other ages are Satya Yuga, Treta Yuga and Dvapara Yuga. The duration and chronological starting point in human history of Kali Yuga has given rise to different evaluations and interpretations. According to one of them, the Surya Siddhanta, Kali Yuga began at midnight (00:00) on 18 February 3102 BCE in the proleptic Julian calendar, or 23 January 3102 BC in the proleptic Gregorian calendar. This date is also considered by many Hindus to be the day that Krishna left Earth to return to his abode. Most interpreters of Hindu scriptures believe that Earth is currently in Kali Yuga. Many authorities such as Swami Sri Yukteswar, and Paramhansa Yogananda believe that it is now Dvapara Yuga. Many others like Aurbindo Ghosh have stated that Kali Yuga is now over. The Kali Yuga is sometimes thought to last 432,000 years, although other durations have been proposed.

Kālī (Sanskrit: काली, IPA: [kɑːliː]; Bengali: কালী; Punjabi: ਕਾਲੀ; Tamil: காளி; Telugu: కాళికాదేవి; Kannada: ಕಾಳಿ ಮಾತೆ), also known as Kālikā (Sanskrit: कालिका, Bengali: কালিকা), is the Hindu goddess associated with empowerment, shakti. The name Kali comes from kāla, which means black, time, death, lord of death, Shiva. Kali means "the black one". Since Shiva is called Kāla—the eternal time—Kālī, his consort, also means "Time" or "Death" (as in time has come). Hence, Kāli is considered the goddess of time and change. Although sometimes presented as dark and violent, her earliest incarnation as a figure of annihilation still has some influence. Various Shakta Hindu cosmologies, as well as Shākta Tantric beliefs, worship her as the ultimate reality or Brahman. She is also revered as Bhavatārini (literally "redeemer of the universe"). Comparatively recent devotional movements largely conceive Kāli as a benevolent mother goddess.

Kālī is represented as the consort of Lord Shiva, on whose body she is often seen standing. She is associated with many other Hindu goddesses like Durga, Bhadrakali, Sati, Rudrani, Parvati and Chamunda. She is the foremost among the Dasa Mahavidyas, ten fierce Tantric goddesses.

Yuga (Devanāgari: युग) in Hindu philosophy is the name of an 'epoch' or 'era' within a cycle of four ages. These are the Satya Yuga, the Treta Yuga, the Dvapara Yuga, and finally the Kali Yuga. According to Hindu cosmology, life in the universe is created, destroyed once every 4.1 to 8.2 billion years, which is one full day (day and night) for Brahma. The lifetime of a Brahma himself may be 311 trillion and 40 billion years.[1] The cycles are said to repeat like the seasons, waxing and waning within a greater time-cycle of the creation and destruction of the universe. Like Summer, Spring, Winter and Autumn, each yuga involves stages or gradual changes which the earth and the consciousness of mankind goes through as a whole. A complete yuga cycle from a high Golden Age of enlightenment to a Dark Age and back again is said to be caused by the solar system's motion around another star.

Lord Vishnu has many avatars and in each yuga,he has revealed all of them except-the last avatar(tenth)-Kalki.It is said that in the last yuga Lord Vishnu will reveal this avatar too and the Kalki avatar will lead to the end of the world.The main reason is to destroy the wicked,to restart the new creation,and to restore the purity of conduct in people's life. This avatar will be seated in a white horse with a drawn sword blazing like a comet.