Shortly after the Siddhi day in November 1926, Sri Aurobindo retired from daily contact with his disciples and placed the Mother in charge of their care. Thereafter he saw them only a few times a year on what came to be known as Darshan days. The Sanskrit word "Darshan" means "seeing" and refers, in this context, to seeing Sri Aurobindo and the Mother and to receive their blessings.

At first there were three Darshan days: the Mother's birthday, Sri Aurobindo's birthday, and the Siddhi day. In 1939 a fourth day was added: the Mother's final arrival in Pondicherry. On these occasions, Sri Aurobindo and the Mother sat together in a small room, while the sadhaks and devotees approached one by one and offered flowers and bowed down at their feet.

After Sri Aurobindo left his body in 1950, the Mother continued to give Darshan on these days. From 1963 onwards, she gave Darshan from the terrace for five or ten minutes as she gazed upon those who had gathered in the street below.

The rest is here:

The Sri Aurobindo Ashram - Important Dates