As defined on Soompi, idol is a “general term for young K-Pop entertainers. What sets them apart from normal “singers” is that they are also trained to do other things such as act, MC, DJ model and dance.”

Differently from Western entertainers, k-pop idols are trained since their childhood/early teenage years in order to acquire the skills needed for their careers. The ascend to idol status is further explained on many articles and posts, one of which we’ll quote, written by Reddit user gonline:

“People audition, or can be "spotted" by scouts - if they have a look the label is interested in. It differs for each agency. There's hundreds, so it's impossible to give an exact answer. Trainees train for different amount of years, for a different amount of reasons that is individually based. Some can train for 7 (usually start as kids) and some can do months before debuting. It's all qute context based. Training would be dancing, singing/rapping, or acting. Language if you're not Korean born, but that's not shocking. Again, context based.

If one trainee is the lead singer, they will focus more on vocals with them. If they are of school age (which they would be), they are still expected to attend school and all that. Trainee contracts are usually short term however, so if the label thinks you haven't progressed, or even if it's not for you, you have an easy out. It's not a seedy money making service. If you do stick it out and debut, then you live in a dorm. How nice it is is relative to how big (rich) the label you are signed to is and how many members you have. Higher labels have nice dorms, while struggling labels have known to give a group tinfoil as curtains.

As for money, they usually don't get paid until they "reimburse" (food, housing, training, gym, school, lessons vocally, etc etc) their label, which is always a gamble, as success isn't guaranteed with the oversaturation of pop groups in Korea. A catchy song with nice visuals isn't always enough. There is money to be made though - obviously. Some of the biggest groups like SNSD make a couple million each (there are eight of them in total). It's not all poverty and tinfoil windows. A lot of idols who got popular (much like any American pop act that got popular) are millionaires and live well off in Seoul (which has a high cost of life). Labels divide income differently. SM takes 60% of artists profits. SNSD is under SM. YG takes 30%. PSY (Gangnam Style) is under YG. But then there are loopholes and conditions per artists that might favour them. Again, it's hard to speak in a general sense. They might take 100% for themselves if it's an out of country tour, or if it's a different style of performance (think they got cast for Broadway).

Contracts usually last 4-5 years. Again, it depends. People can get out of them, but it usually is a mess in the media and they get slated for being "quitters" and "ruining the group" by fans, etc. Requires lawyers etc. That's not everyone though. SM seems to have the most issue with members leaving their popular groups. I think five (three from one group, one from another and one from a third) have left in the space of this year? Other agencies seem to have less issues with idols wanting to leave, as SM is quite notorious for being shady with money and overworking their idols, to the point of compromising their health. However they are also the fast route to success (mostly). If you debut with SM, you have a LOT of connections and pretty much an established fan base, so you can see why people still go with them.”