A communicable disease can be passed from one person to another, or from one organism to another. It is caused by a pathogen, such as a bacterium or a virus. Cholera, tuberculosis and HIV are communicable diseases, and so is Chalara ash dieback in trees.
A non-communicable disease cannot be passed on. It is not caused by a pathogen, so you cannot catch it from someone else. Cancer, heart disease and type 2 diabetes are examples.
Non-communicable diseases have other causes. These include the genes a person inherits, their diet and lifestyle, and their environment.