Kathina is a Buddhist festival which comes at the end of Vassa, the three month rainy season retreat for Theravada Buddhists. The season during which a monastery may hold a 'Kathina' festival is one month long, beginning after the full moon of the eleventh month in the Lunar calendar (usually October). In order to hold a 'Kathina', a monastery must have had five monks in residence during the retreat period and only those who were present for the entire retreat are eligible to receive the robe cloth offered.
It is a time of giving, for the laity to express gratitude to monks. Lay Buddhists bring donations to temples, especially new robes for the monks. It usually occurs in October and November.
As a Pali term it means hard, firm, unshakeable.