in·fec·tion 
(ĭn-fĕkshən)
(ĭn-fĕkshən)n.
1.
a. The invasion of bodily tissue by pathogenic microorganisms that proliferate, resulting in tissue injury that can progress to disease: measures taken by the hospital to prevent infection.
b. The entry or placement, as by injection, of a microorganism or infectious agent into a cell or tissue.
c. An instance of being infected: developed an infection in my toe.
d. An agent or a contaminated substance responsible for one's becoming infected: an infection spread by contaminated water.
e. The pathological state resulting from having been infected: a drug to control infection.
2. An infectious disease: Crowded conditions gave rise to several serious infections.
3. An instance of a virus or similar software program infecting a computer.
4. The communication of a usually undesirable idea, emotion, or attitude by contact with other people or by example.