It stands for estimated rental value; the opinion of valuation experts/ valuers as to the open market rent, which on the date of valuation (of a real estate property) could be obtained- based on reasonable expectations- on a new lettable property or rent review of such a property. This value reflects the estimated annual market rental value of lettable property, in the open market, as figured out semi-annually by a group of valuers.

It is also known as a market rental value.