A prepared option that is available "just in case" the main option fails.

Other terms that describe a just-in-caser:
- Plan B
- Contingency Plan
- Alternative Measure
- Emergency Option
Jarvis: Why on earth would you buy airplane tickets when we've got cheap train tickets booked and ready to go see the Super Bowl?
Daniel: Relax dude! Airplane tickets are just-in-casers. Remember what happened last year? I don't want train delays causing us to miss half the Super Bowl game ever again.

Nora: You brought both your laptop and the iPad to the business meeting!?! You're not gonna need both!
Bethany: I only brought the iPad as a just-in-caser. I'll be taking notes on the laptop.
by OffBeatDrummer January 6, 2021
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