AIS, or Annual Information Statement, is a more detailed and comprehensive tax department record than Form 26AS, capturing a much wider range of your financial transactions through the year — not just TDS and TCS, but also things like interest earned, dividends received, mutual fund and stock purchases and sales, and even certain high-value transactions reported by banks and other institutions.
AIS is meant to give both you and the tax department a fuller picture of your financial activity, helping ensure your income tax return accurately reflects all your income sources. It's a good idea to review your AIS before filing your return, since it can surface income you might have forgotten to report, such as small amounts of savings account interest or dividend income, helping you avoid discrepancies or future tax notices.