Gazumping: When the seller of a house accepts a higher offer, after agreeing in principle to a lower offer. Gazumping can occur in the long period before house contracts are exchanged. More on Gazumping http://www.mortgageguideuk.co.uk/housing/gazumping-uk.html
Gazundering: This occurs when the buyer waits until just before completion and then lowers their offer.
Gross Income: Total income before tax.
Ground Rent: If the property is leasehold you will probably have to pay ground rent to the person that owns the land you property stands on.
Guarantor: A Guarantor is an individual who agrees to guarantee that a loan will be paid. The guarantor is fully liable for repayment of the loan if the borrower defaults.
Guarantor Mortgages: Due to the credit crunch most lenders will now not offer 100% mortgages. As a consequence, the only 100% mortgage deals readily available are guarantor mortgages.