As per Lawkidunya, Deductible Allowance” means an allowance that is deductible from total income under Part IX of Chapter III;

We also define Deductible Allowances are deductions from salary income to arrive at taxable salary. Amount of Zakat paid in the tax year is deductible allowance from taxable salary. Interest amount eligible for deduction is lower of the amount paid or 50% of taxable income (presumably after deductions u/s 60) or two million rupees.