to lead someone off the right path, or (when it happens to you) to stray from it: literally to wander, and almost always to be deceived away from the truth.
The picture under this word is a person or animal off the path, lost. It can be physical, like a sheep that strays from the flock or travelers lost in the wilderness, but the New Testament almost always uses it for going astray in a deeper sense: drifting away from the truth, from God, or from the right way to live.
The word works in two directions, and the same verb covers both. Used of what one person does to another, it means to mislead or deceive, to pull someone off course on purpose. Used of what happens to a person, it means to be led astray, to be taken in, to err. So a false teacher does this to his hearers, and the hearers in turn have it done to them.
Because the danger is so often a deliberate deceiver, the New Testament rings with the warning "do not be deceived," and the figure of the great deceiver in Revelation is the one who leads the whole world astray. The thread tying every use together is simple: someone is off the path who should be on it, and the question is who pulled them off and how to get back.