NTR is shorthand for a Japanese porn term, netorare. (To be fair, many use it as shorthand for the very similar Japanese concepts, netori and netorase, as well, but we’ll get into that later.)
Netorare is often equated to cheating or cuckolding, though it’s a bit more specific than cheating and a bit different than cuckolding (though there can be some overlap). The word “netorare,” as well as “netori” and “netorase,” ultimately derives from a verb that means “to take” or “to steal,” which should give you the basic idea: it refers to a person being stolen from someone close to them (usually a lover, though it can encompass other types of relationships—common alternatives are family members and crushes). This “theft” happens on a sexual level at the bare minimum, and often on a more emotional level as well.
Generally speaking, the most common examples of this fetish center around a person (Party A) who cares deeply for the person close to them (Party B), but who through some combination of seduction, trickery, blackmail, threats, and/or force is compelled to sleep with someone else (Party C). Party A will ultimately become so enamored of Party C’s sexual prowess that he/she is willing to ignore or even abandon the previous relationship with Party B. (If Party B is Party A’s lover, Party C’s sexual prowess is almost always far superior to Party B’s.) There are different scenarios, of course, but this is far and away the most common, and usually alternate scenarios are little more than variations.
It’s worth noting that Party C does not need to be a single person, and sometimes Party A has no specific loyalty to Party C afterwards, in which scenario Party C acts more in the capacity of awakening Party A to greater sexual pleasures than Party A had been familiar with, after which Party A will typically seek those pleasures out wherever he/she can find them.
For a more in depth explanation of specific terms, please open the spoiler below.
