"Bhagvad" is Sanskrit for "God" and "Gita" is Sanskrit for "song". Bhagvad Gita, then, translates to "Song of God".
Bhagvad Gita is comprised of 700 verses in 18 chapters. It is a part of the epic poem, Mahabharat. To fully appreciate the Bhagvad Gita, one must first understand its context in Mahabharat.
Mahabharat is an extension of the original 24,000-verse Sanskrit poem entitled "Bharat", written by Vyaas probably around 800 BCE. That extension added more than 64,000 verses bringing the total to over 90,000 verses. So vast is the Mahabharat's coverage that in its first chapter is the claim of all-inclusiveness: "What is found here, may be found elsewhere. What is not found here, will not be found elsewhere."
Mahabharat is the account of King Bharat's dynasty and the struggle for the throne of Hastinapur. The two princes claiming to be legitimate heirs to the throne are Yudhishtir (son of King Pandu and Queen Kunti) and Duryodhan (eldest son of King Dhritarashtra and Queen Ghandhari). Younger brother to Dhritarashtra, Pandu still ascended to Hastinapur's throne because of Dhritarashtra was blind in both eyes and deemed unfit to rule. King Pandu, though, died early into his reign and, by default, Dhristarashtra was appointed caretaker of the throne until Yudhistir, King Pandu's eldest son, was old enough and deemed fit to be king.
The struggle for Hastinapur's throne culminates in the great battle of Kurukshetra. And it is just before the start of this battle where Arjun, Yudhishtir's brother and supreme archer, loses heart in the prospect of battling and likely killing his cousins. Here, he turns to Krishn - his friend, his charioteer and also his cousin (Kunti's brother's son) - to ask Him of the logic in fighting his own family.
In the sixth parva (or book) of Mahabharat, from chapters 25 to 42, Krishn Bhagwan answers Arjun's dilemma. In this process, He also reveals a condensed treatise on the Vedas. The five primary philosophical subjects covered by Krishn Bhagwan are:
These subjects are covered in 18 chapters:
Traditionally, Mahabharat is set in the very latter stage of Dwapar Yug, placing it at about 5,500 years back or 3500 BCE. Krishn Bhagwan's passing, at age 125 and well after the end of the great war, is widely believed to be the start of Kali Yug.