What is the difference between air-conditioning and ventilation?

Ventilation is supposed to deliver fresh outdoor unit to the premises and remove impurities and unpleasant odours. Remaining in a room without proper ventilation  is uncomfortable. Ventilation is an essential element.

Air-conditioning is responsible in particular for maintaining the proper temperature and humidity level in specific room. It is used much more frequently in summer months, primarily to lower the temperature. 

It is important that the ventilation and air-conditioning work well together, because their operation can be mutually exclusive (e.g. in summer months).