Used to label an unusually large number of occurrances of a disease or condition in one place. An autism cluster would be an unusually large number of cases of autism in (perhaps) a single locality. Clusters constitute evidence in the search for causes of diseases and conditions.
Top definition. jawn. a word used by Philly cats to describe anything and everything. NY cats interject with the word joint but it doesn't convey the same feelings.
'Jawn' is one Philly thing New York can't lay claim to. When I moved from North Carolina to Philadelphia a few years ago to teach at Gwynedd-Mercy College, I noticed a lot of things that were unique to the city. The way natives say wooder ice, the devotion to pretzels and cheesesteaks, and ... jawn.. The most interesting and unique Philly word has to be jawn.