"concrete" can be used as an adjective to mean "specific" e.g. to give a concrete example,..." "concrete over" is a verb to describe the activity of putting concrete over an area of the ground e.g. "they concreted over the lawn to make a patio" An "infestation" is an invasion of a particular place, often by rodents (e.g. rats, mice) or damaging bacteria e.g "that old house is infested with rats / it has had rat infestation problems. "exponentially" is a mathematical word which has a specific mathematical meaning which I can't totally remember now. A normal increase is "arithmetical" 1, 2, 3 etc. An "exponential" increase is much faster e.g. 10, 100, 1000. When used in ordinary language, it just means a very quick and large increase. e.g. "visitors to the West Ham United Football Club website rose exponentially after they beat Manchester City."