Something that’s random is lacking in order, plan, or purpose. It happens totally by chance, like the random picking of lottery numbers or unplanned random acts of kindness.
Sometime in the 1980s, teenage slang hijacked the adjective random and tried to turn it into a word meaning weird, odd or out of place. As in "Dude! That guy wearing purple spandex at the party was so random!" But don't fall for it. Something that’s truly random is totally governed by chance and has no specific pattern, like choosing a card at random from a magician’s deck.
adj lacking any definite plan or order or purpose; governed by or depending on chance
positive recurrent aperiodic state of stochastic systems; tending in probability to a limiting form that is independent of the initial conditions
dependent upon or characterized by chance
being or having a random variable