| focus-forming unit | A measurement of the concentration of live virus in a given amount of fluid. This is measured by spreading a known amount of the fluid over a layer of cultured cells which are infected by the virus, then counting the number of areas in the culture which look infected. (09 Oct 1997) |
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| focus groups | A method of data collection and a qualitative research tool in which a small group of individuals are brought together and allowed to interact in a discussion of their opinions about topics, issues, or questions. (12 Dec 1998) |
| focus, principal | <physics> The point at which a lens focuses an axial object point. Synonymous with focal point. (05 Aug 1998) |
| Friend spleen focus forming virus | <virology> Defective virus found in certain strains of Friend virus, detected by its ability to form foci in spleens of mice and believed to be responsible in those strains for the production of a leukaemia associated with polycythaemia rather than anaemia. (18 Nov 1997) |