There is a fine line between maintaining a good working relationship with a superior and becoming an overly ambitious toady, lackey, or suck-up. The act of using excessive flattery and other shallow behavior towards a superior strictly for professional or personal gain is known as brown nosing, and it is routinely denounced as a desperate ploy for attention in business circles. Some bosses may respond well to this behavior, but others see it as a marginal employee's attempt to climb the corporate ladder ahead of more deserving candidates.
Brown nosing gets its name from a rather rude, even if appropriate, source. Kissing up or sucking up to a boss, especially in a very obvious and shallow manner, can also be called kissing the boss' butt. It quite literally refers to the remnants of fecal matter that would linger if such a degrading and humiliating act were actually performed. The term suggests a willingness to perform any act, no matter how degrading or repulsive, in order to curry favor with a superior.
Not all complimentary overtures towards a superior can be construed as brown nosing, although in the realm of office politics, anything is possible. A jealous or ambitious co-worker could always make an accusation of sucking up, even if the actual behavior did not reach the level of manipulative flattery associated with the act. Because the practice has a very negative connotation, many employees choose to keep their interactions with a superior on a very professional level. An employee may have a close working relationship with a superior, but such familiarity should not be confused with being a toady.
Brown nosing is not limited to the business world, however. Some students may use flattery or attention in order to impress or influence a teacher, for example. The difference between sincere compliments and something more excessive is generally a matter of intent. An individual may be fully aware of his or her obnoxious or overly ambitious behavior, but also believes that his or her efforts will be rewarded with a promotion or other professional gain. There may actually be little to no personal interest in the superior himself, but this behavior is not about the journey as much as it is the destination.