Thermodynamics is the study of the movement of heat. If you touch a block of ice, it isn't always pleasant unless it's a really hot day. If you touch a hot pan out of the oven you'll burn yourself. Both of those things happen because of how fast heat is moving. The heat from the hot pan moves into your hand rapidly, and when touching an ice cube you lose your own body heat fast. Heat transfers from hot places to cold places - or in other words, heat spreads out. Extreme cold or heat can damage our tissues, so it's a pretty important thing to understand. It's also how we've been able to build refrigerators and large insulated coolers to take to the beach.
When the system undergoes change from one thermodynamic state to final state due change in properties like temperature, pressure, volume etc, the system is said to have undergone thermodynamic process. Various types of thermodynamic processes are: isothermal process, adiabatic process, isochoric process, isobaric process and reversible process. These have been described below.
When the system undergoes change from one state to the other, but its temperature remains constant, the system is said to have undergone isothermal process. For instance, in our example of hot water in thermos flask, if we remove certain quantity of water from the flask, but keep its temperature constant at 50 degree Celsius, the process is said to be isothermal process.
The process, during which the heat content of the system or certain quantity of the matter remains constant, is called as adiabatic process. Thus in adiabatic process no transfer of heat between the system and its surroundings takes place. The wall of the system which does not allows the flow of heat through it, is called as adiabatic wall, while the wall which allows the flow of heat is called as diathermic wall.
The process, during which the volume of the system remains constant, is called as isochoric process. Heating of gas in a closed cylinder is an example of isochoric process.
The process during which the pressure of the system remains constant is called as isobaric process. Example: Suppose there is a fuel in piston and cylinder arrangement. When this fuel is burnt the pressure of the gases is generated inside the engine and as more fuel burns more pressure is created. But if the gases are allowed to expand by allowing the piston to move outside, the pressure of the system can be kept constant.