a function that satisfies the property that it is computationally infeasible to compute the input from the result

a mathematical formula that is easy to solve in one direction but difficult solve in the other

a mathematical function that is significantly easier to compute in one direction (the forward direction) than in the opposite direction (the inverse direction)

a mathematical operation easy to conduct in one direction, but almost impossible to conduct in the reverse

an invertible function that is easy to compute but computationally difficult to invert

a relation between two objects A and B such that B can be readily calculated from A, while there is no computationally feasible way of determining A from a knowledge of B

A function that is easy to compute in one direction but quite difficult to reverse compute (compute in the opposite direction).

A one-way function is a function that is easy to compute but hard to invert — given the output of the function it is difficult to find any input which yields this output.