The LAC is the commonly used abbreviation for the Line of Actual Control which is a loose demarcation of sort, separating Indian and Chinese controlled territories. In India, it borders Ladakh, Himachal Pradesh, Sikkim, Uttarakhand and Arunachal Pradesh while in China, its borders the Tibet Autonomous Region.
The LAC was officially agreed upon in a bilateral agreement in 1993 but it was first used in 1959 between the then Chinese premier, and the Indian Prime Minister. The unofficial demarcation was used for cease-fire post the 1962 Sino-Indian war.
The 1993 bilateral agreement (Agreement On The Maintenance Of Peace Along The Line Of Actual Control In The India-China Border) in broad, simple terms, was an agreement which essentially ensured :
Less military presence and reduction of forces
Development of measures so as to not violate aerial intrusion
Friendly agreements in case of conflict
Bilateral negotiations in order to decide the length, extent, placement of the LAC
Disallowance of military exercises and drills
Despite the intentions of agreeing upon a common border, this has not been done yet. India allegedly follows a boundary similar to the Johnson line of 1865, while China follows one similar to the Macartney-Macdonald line of 1899.
The India-China border standoff over the past few weeks has become a cause of worry. Following the clash in the Galwan Valley due to the construction of the new Galwan Bridge, increased military action has taken place at the LAC consisting of a deadly clash in which 20 Indian Soldiers were reported dead.
I hope you understood the basics of the Line of Actual Control, feel free to ask me any questions about it.
Till Next time,
The Alpha Theory