In simple term paying taxes in "Installments" rather than in lump sum while filing ITR. Tax amount paid before 31st March of respective FY is considered as an advance tax.
Tax is to be paid before certain due dates given by @IncomeTaxIndia
Q. Applicability of Advance Tax ?
Advance tax applicable to all assesses whose tax liability in a year exceeds Rs.10,000
Assessees include Salaried people, Businesses, Freelancers, Traders etc. This means all assesses.