Short answers, pulled from the story.
The Majjhima Nikaya is a Buddhist scripture collection whose name means "Collection of Middle-length Discourses." It is the second of five nikāyas in the Sutta Pitaka, one of the three baskets of the Pali Tipitaka of Theravada Buddhism. It contains 152 discourses attributed to the Buddha and his chief disciples.
The Majjhima Nikaya was composed between the 3rd century BCE and the 2nd century CE.
The Majjhima Nikaya contains 152 discourses arranged in three parts, each with five divisions. All divisions except the penultimate one contain ten discourses.
The Chinese parallel is known as the Zhong Ahanjing, a complete translation of the Sarvastivadin recension of the Madhyama Agama found in the Chinese Buddhist canon. This version contains 222 sutras, compared to the 152 suttas in the Pali Majjhima Nikaya.
Full English translations were produced by Lord Chalmers (Further Dialogues of the Buddha, 1926-1927), I.B. Horner (The Book of Middle Length Sayings, 1954-1959), David W. Evans (1991), and Bhikkhu Sujato (The Middle Discourses, 2018). Bhikkhu Sujato's translation was published on SuttaCentral and released into the public domain.
Bhikkhu Bodhi, in the introduction to his translation, described the Majjhima Nikaya as the collection that combines the richest variety of contextual settings with the deepest and most comprehensive assortment of teachings among all books of the Pali Canon.