What is PICO ?
The PICO framework helps you to formulate and structure your foreground question, breaking down a clinical scenario and enabling you to effectively trace the most relevant information sources you require for your research.
PICO is the acronym for Patient Intervention Comparison Outcome.
Examples of questions that it may be used for (not a conclusive list):
Treatment: establishing whether a particular treatment would benefit a patient
Diagnostic: confirm or exclude a diagnosis
Prognosis: estimate the likely course of a medical condition
Prevention: reduce the chances of disease by identifying risk factors

Gerrish, K. and Lacey, A. (eds.) (2010) The research process in nursing. 6th ed. Chichester: Wiley-Blackwell.
Further examples of PICO questions:
List of PICO questions - Recommendations for Management of Common Childhood Conditions - NCBI Bookshelf (nih.gov)