Encumbrance certificate is the certificate issued by the Registrar pertaining to a particular piece of land about the transaction made during the period you apply for.

If there was sale, mortgage, settlement, Will, Gift or other deeds etc and the parties executed and beneficiaries, date of transaction, amount etc will be there for that period.

since builder has given you the EC you can after obtaining opinion from your lawyer purchase the property . obtain a certificate from your lawyer that title is clear and marketable . then take a call

At the time of selling your property or buying a new property you need to check the track of the property and verify the genuineness of your seller. Government registry enters all these details in the registrar of books. You can visit the concerned register office and file an application with a small fee. They will provide with up to date of the property details. This is called encumbrance certificate.Some offices are equipped with Online facilities also.