ELI5: Explain Like I'm 5
Examples: binomial inverse theorem, what is the difference between shia and sunni, corporate balance sheet, compound interest, trinary logic

Countermeasure

A countermeasure is like an umbrella against the rain. It helps keep bad things from happening. For example, in a computer system, a countermeasure would be a tool to help stop hackers from getting in and stealing information. It would make sure that the system is secure and only people with the right passwords can get in.