A code gadget is any pre-existing string of binary code in an executable that by chance happens to have some specific properties that make it possible to be rep

A code gadget is any pre-existing string of binary code in an executable that by chance happens to have some specific properties that make it possible to be repurposed by an attacker, usually by jumping in the middle of it. IIRC the term was introduced with the Return Oriented Programming style of attacks and reused for spectre-like speculation attacks.