Tulsi Vivah is a Hindu ceremonial marriage of the holy Tulsi plant (considered a manifestation of the goddess Lakshmi) to Lord Vishnu or his avatar Shri Krishna.
It marks the symbolic union of the two and is an important ritual in Hindu culture.
This event usually takes place on Prabodhini Ekadashi (the 11th day of the waxing moon in the Hindu month of Kartik), which signifies the end of Chaturmas (the four months during which auspicious events like marriages are avoided).