Roleplaying is the act of playing out the role of a character: describing their actions and thoughts, and speaking for them, to interact with an imaginary setting.
Roleplay is also referred to as a style of gaming. Most computer based RPGs have several styles of play available, and Neverwinter Nights is no exception. People who prefer to roleplay will often gravitate towards servers that provide detailed environments that are true to the setting on which it is based, and where likeminded players are around to interact with.
Roleplay is also a reference to a style of game server or persistent world, one that is geared towards roleplaying in general, where combat has a purpose, is sparse, and likely more dangerous and full of risk.