School holiday in Chennai today, October 21, is due to heavy rain, causing the shutdown of schools. The Economic Times reports that schools in Chennai have been closed as a precautionary measure following the heavy rainfall in the city. This decision aims to ensure the safety of students and staff. The article does not provide information on the specific duration of the school holiday or any state-wise closure updates. It only mentions that schools in Chennai have been shut down due to the heavy rain. The exact details of the school holiday, such as the reopening date or any alternative arrangements for students, are not provided in the available evidence.