random

Without a systematic pattern or discernible sequence in its behavior or occurrence. Events or data series are said to be random when they lack specific direction, and cannot be explained or predicted except by chance or in a probabilistic or statistical manner.

"TANSTAAFL" is the term coined by Robert Heinlein in his 1966 book, "The Moon is a Harsh Mistress." Whenever anybody that you do not know offers you something free, that is most likely because they want something in return. Therefore, be wary of the email solicitations claiming that you are a winner of a random lottery or those emails where somebody is trying to give you money but needs your bank account number. After all, "There Ain't No Such Thing As A Free Lunch."