The standard deduction is a flat amount automatically subtracted from a salaried person's or pensioner's income before tax is calculated, with no need to submit any bills, receipts, or proof to claim it. It exists to give salaried and pension-earning taxpayers a basic deduction roughly comparable to the business expense deductions that self-employed individuals can claim.
The good news is that the standard deduction is available under both the old and the new tax regime, unlike most other deductions which are largely restricted to the old regime only. Because it requires no paperwork and is applied automatically, it's one of the simplest tax benefits to take advantage of — you don't need to do anything special to claim it beyond having salary or pension income.
Because it applies automatically without any conditions attached, it's one deduction almost every salaried taxpayer ends up benefiting from, quietly lowering their taxable income each year without any extra effort.