Incubation Period vs Contagious Period
Incubation (Lat. incubationem = a lying upon eggs) period is the time from exposure to a microbe (like influenza virus) to the appearance of the first symptoms. It is important to note that even though a person may be exposed to a microbe, they may not be infected with it and therefore there will be illness.
Contagious (Lat. contingere = touch closely) period is the time during which an infected person is able to spread an infection to others. This may be through physical contact (touch), sexual transmission, droplet spread (cough/sneeze) or even sharing of personal items.