The uses statement is a declaration by a Pascal program that it will invoke or use certain procedures, functions, objects, constants, variables and other items which are defined or declared in the specified unit. Uses is a reserved word.
Every pascal program and unit has an automatic implied uses statement of
except in the case where a compiler parameter allows a unit to exclude a reference to the System unit. (One example of this would be if one was recompiling the System unit, it would be necessary for it not to invoke itself.)