Use to which the insured car is put.
There are no 'use' or usage clauses which are universally accepted by car insurers when defining car insurance usage risk and these may vary from car insurance company to company. When asking for a quote it is important to define exactly what you are going to use your car for in order to avoid claims bveing repudiated.

Examples of the main usage types are:

Social, Domestic & Pleasure Only – Use for Social, Domestic & Pleasure purposes excluding use for journeys between home and permanent place of work or any other place of work.

Social, Domestic & Pleasure Including Commuting - Social, Domestic & Pleasure purposes including use by the insured for journeys between home and permanent place of business providing business calls are not made during the course of the journey.

Business Use

Class 1 - Social, Domestic & Pleasure purposes and use by the insured in person in connection with his/her business or profession, excluding commercial travelling or the carriage of goods or samples in connection with any trade or business.

Class 2 - Social, Domestic & Pleasure purposes and for the business of the insured and the insured’s employer or partner excluding commercial travelling.

Class 3 - Social, Domestic & Pleasure purposes and for the business of the insured and the insured’s employer or partner

Note all the above classes of use Exclude use for hiring, the letting on hire, the carriage of passengers or goods for hire or reward, racing, pacemaking, use in any contest, reliability or speed trail or use for any purpose in connection with the motor trade.

Annual Mileage
Other things being equal it is reasonable to assume that a car which is driven for 16000 miles per year is more of a risk than one driven for only 5000 miles, simply because the car is on the road much more and thus 'exposes' the Car Insurance company to potential liability to a far greater extent.