noun

• (obsolete) A thing whose name cannot be remembered; thingamajig, doohickey.
  "Then the names of all the other things on board a ship! I don't know half of them yet; even the sailors forget at times, and if the exact name of anything they want happens to slip from their memory, they call it a chicken-fixing, or a gadjet, or a timmey-noggy, or a wim-wom—just pro tem., you know."
• (informal) Any consumer electronics product.
  "From the Marvel Mixmaster to the Miracle Microwave, every time a new-fangled gadget has lobbed into the Aussie kitchen, Aussie mums have changed their cooking styles accordingly."
• (computing) A sequence of machine code instructions crafted as part of an exploit that attempts to divert execution to a memory location chosen by the attacker.
  "A Spectre gadget was found in the Linux kernel's implementation of system interrupts."
• (computer science) A technique for converting a part of one problem to an equivalent part of another problem, used in constructing reductions.
  "We reduce an instance of 3-SAT to an instance of bird-flock-optimization, using a gadget that converts each conjunctive Boolean clause to a group of birds."