Pressure:

           The force acting normally per unit area on the surface of a body is called pressure.

Thus    

Pressure P  = $\frac{Force}{Area}$ 
Or                            P = $\frac{F}{A}$  

   
Unit of Pressure:
            In SI units, the unit of pressure is $Nm^{-2}$ also called pascal (Pa).

Thus
1 $Nm^{-2}$ = 1 Pa