Initialism of Crime Scene Investigation (a term of forensic science)
"The suspect was interviewed by the CSI team at the crime scene to gather evidence."
In plain English: CSI is an abbreviation for crime scene investigation, which refers to the process of collecting and analyzing evidence at a place where a crime has occurred.
"The police CSI team arrived at the scene to collect evidence for their investigation."
Initialism of Committee for Skeptical Inquiry (formerly CSICOP)
"The csi organization recently published a report debunking several popular paranormal claims."