TDS is tax deducted at source. There are certain categories of income where TDS is deducted like salary income, interest income, rental income etc.
People who deduct TDS from your income have to provide you with a TDS certificate - Form 16A which has the details of amount deducted.
You can also check it on 26AS online once the deduction details are uploaded.
http://incometaxindia.gov.in/26ASTaxCreditStatement.asp
One way to avoid TDS deduction is to submit form 15G/15H. It helps in avoid TDS in certain categories like Bank and FD interests etc.