- 50 is an even composite number.
- 50 is the number of known Mersenne primes and perfect numbers.
- 50 is the number of US states.
In Greek-based number-naming systems, 50 is associated with prefix "pentaconta-", and with prefix "quinquaginti-" in Latin systems.
- Some currencies, such as the euro, the Israeli new shekel (shekel-wise) and the United States dollar, have banknotes with this number in the denomination.
- Some currencies, such as the Czech koruna, the Israeli new shekel (Agorot-wise in the half-shekel coin) and the Hungarian forint, have coins with this number in the denomination.
It is also the prize for correctly answering the first question in the German game show Wer wird Millionär? in euros.
There is a fifty-move rule preventing endless chess games.