the prosecution; prosecuting side
Refers to the party bringing a criminal case, typically in a legal context. Often contrasted with 弁護側 (the defense).
The prosecution argued for the defendant's guilt.
A witness for the prosecution testified in court.
検察側 is a more common term for the prosecution in criminal cases; 訴追側 is a formal or legalistic synonym.
Compound of 訴追 (そつい, 'prosecution') and 側 (がわ, 'side'). 訴追 is a legal term for bringing a case, from 訴 (そ, 'accuse') and 追 (つい, 'pursue').