An economic activity is a process that, based on inputs, leads to the manufacture of a good or the provision of a service. The classification of activities divides economic activities into categories which, by aggregation, make it possible to define the sectors of activity (Agriculture, Industry, Construction, Trade, etc.). The units in which business statistics are concerned (enterprises, legal units, establishments, etc.) may carry out one or more economic activities, but each unit has only one main activity. The sectoral classification of a unit corresponds to the sector of activity to which its main activity belongs. In labour force or employment by activity statistics, individuals are classified according to the main activity of the establishment or enterprise that employs them. This establishment may be different from the one where they work, particularly for temporary workers, employees of cleaning companies and equipment maintenance services.