A continent is a large landmass in Second Life composed of a group of more then thirty individual sim regions, placed in direct contact to eachother. Users can then travel from one sim to another by crossing the sim's borders. Unlike isolated sims, the geographical features (as well as transportation links such as roads, railways and waterways) continue from one sim to another, forming a large multi-sim structure which resembles one large island.
Currently there are nine major linden-designed (official) continents - often referred to as "mainland continents" - within Second Life: Sansara (the original continent), Heterocera Atoll, Jeogeot, Satori, Blake Sea, Nautilus, Corsica, Gaeta I, Gaeta V, Zindra (which due to its adult content will not be discussed here), Eden, Estate and Sharp .
There are also a number of unofficial continent-like landmasses and subcontinents (minus of 30 sims) created by private individuals and groups (typically known as Estates). Here you will find a list of the various continents and their open airports.