Final answer:
A communicable disease is an illness that can be spread from one person to another, often caused by pathogens such as bacteria or viruses. Infectious diseases that are communicable are sometimes referred to as contagious due to their ease of transmission between individuals.
Step-by-step explanation:
A communicable disease refers to an illness that can be spread from one person to another. Such diseases are often caused by pathogens such as bacteria, viruses, parasites, and fungi. These illnesses can be spread through a variety of mechanisms, including direct contact, airborne transmission, or through vectors such as insects. Infectious diseases like measles and the common cold are communicable and contagious, as they are easily transmitted between individuals. In contrast, noncommunicable diseases are not spread from person to person and can include conditions like tetanus or Legionnaires disease which are caused by pathogens that are contracted through other means.