What is the Standing Instruction given in the demat account opening form?

In a bank account, credit to the account is given only when a 'paying in' slip is submitted together with cash/cheque. Similarly, in a depository account a 'Receipt in' form has to be submitted to receive securities in the account. However, for the convenience of investors, facility of 'standing instruction' is given. If you say 'Yes' for standing instruction, you need not submit 'Receipt in' slip every time you buy securities.