Implied topless involves the model being topless in the image, but hiding the nipples with posing, lighting and/or props.
Implied nudity involves the model being nude in the image, but hiding the more sensitive parts of the body including the nipples and genitals with posing, lighting and/or props.
Implied nudity is my specialty, and is the style I focus on the most nowadays.
Topless fully exposes the breasts and nipples.
Full nude shows no bounds in terms of nudity.