Definition - What does Cold Front mean?
A point where a large mass of warm air collides with a large mass of cold air is known as a cold front. At the cold front, the density of the colder air causes the warm air to be pushed upwards, creating an area of low pressure.
Safeopedia explains Cold Front
Due to the higher density of cold air as compared to warm air, the cold air will sink under the warm air and occupy the space there. The warm air has no choice but to rise, creating low pressure due to the loss of warm air. If the warm air contains moisture, a large amount of clouds will form when the warm air is pushed above a certain level as the moisture in the air turns into water droplets around dust particles, forming clouds. In cases where the cold air is moving at a high speed and the difference in temperature between the two bodies of air is significant enough, the favorable conditions may result in severe hailstorms and even tornadoes.