'Impurity' in the Bible

It is actually reported [everywhere] that there is sexual immorality among you, a kind of immorality that is condemned even among the [unbelieving] Gentiles: that someone has [an intimate relationship with] his father’s wife.

Run away from sexual immorality [in any form, whether thought or behavior, whether visual or written]. Every other sin that a man commits is outside the body, but the one who is sexually immoral sins against his own body.

But because of [the temptation to participate in] sexual immorality, let each man have his own wife, and let each woman have her own husband.