MacGyverisms are the acts of makeshifting and klugework that Angus MacGyver is best known for. These are probably the best-remembered part of the late-80s/early-90s TV series MacGvyer.
Some of the more noteworthy MacGyverisms involved using some ammonium nitrate fertilizer and diesel fuel to make some small bombs for distractions, and melting ice with a light bulb to flood a lock, breaking it when the water re-froze. Some of these tricks were pure bullshit, and wouldn't work at all, while others would work perfectly as stated (like the lock-breaking ice-wedge, for the right kind of lock). Most common though, were tricks that were almost right, missing some minor step needed to make them really work.