A DIS (Delivery Instruction Slip) is the cheque-book of the demat world: a signed instruction from a shareholder to their Depository Participant to debit shares from their account and deliver them to a buyer's account. For unlisted shares, the seller submits a DIS (physical or electronic, e.g. CDSL "easiest") quoting the ISIN, quantity and the buyer's BO ID.
Why it matters to you
As a buyer, the DIS is the mechanism by which the seller actually delivers your shares in an off-market transfer. You should release full payment only against confirmed receipt in your demat — or use an escrow-style platform that sequences payment and delivery for you.
Example: A seller filled the DIS with the wrong target ISIN, sending the wrong scrip; always cross-check the ISIN on the slip before it is submitted.