Adverb
according to need (physicians use PRN in writing prescriptions)
Source: WordNetIt takes a good deal of physical courage to ride a horse. This, however, I have. I get it at about forty cents a flask, and take it as required. Stephen Leacock
Regardless of the response from the Jewish person, we remain friends in support of the State of Israel as required by scripture. Jerry Falwell
• Top down implies level of detail that is, looking at the highest level of summarization and then decomposing hierarchically to lower levels of detail as required. John Zachman
My first two books, Letters to a Young Brother and Letters to a Young Sister, were... distributed pretty widely. Judges in juvenile justice facilities started citing the book as required reading. Hill Harper
add water as needed Source: Internet
About 100 members went through the necessary registration, screening and testing as required by the health department. Source: Internet