What is definition of Standard deduction ?

I assume you are asking this question based upon the proposed standard deduction put forth by FM Arun Jaitley at the budget presentation in parliament on Feb 1. Essentially, standard deduction refers to an amount which is deducted from the annual salary while evaluating the income tax liable for salaried employees. For instance, the current tax slab is 3 LPA. If your salary is 3 LPA, you will have to pay a certain amount of tax. However, due to standard deduction, your effective salary evaluated will be 2.6 LPA (3.0 LPA - 40,000). Thus, you will not have to pay any tax due to standard deduction. However, the recently intoduced budget takes away Rs. 19,200 as transport allownace and Rs. 15,000 as medical allowance. Thus, the effective deduction is this instance becomes (Rs. 40,000 - (Rs. 19,200 + Rs. 15,000)) which comes out to Rs. 5,800/- Thus, the effective standard deduction for salaried employees comes down to Rs. 5,800/-