Transcribing is the act of learning a piece of music by ear from a recording or live concert without sheet music. In jazz, as well as virtually all other styles of music, transcribing is a key part in developing ‘language’. We use the word language when talking about this because jazz is a language; top jazz improvisers are not making it up on the spot with unique ideas every solo, rather, they have learned many solos from a myriad of different recordings and pull from their vast bank of collected phrases. They have taken what they transcribed, distilled the solos down into usable phrases for themselves, and then implemented those phrases into their own playing. After a period of time of digesting that solo, those phrases they learned start to sound more natural and become part of them, and then come out spontaneously, a.k.a improvised. This is also how we learn languages; we learn small fragments at a time and slowly start to use them in sentences. As your sentences become more complex, the words and phrases you learn can also become more complex, which makes the way you speak slowly start to sound more articulate and rich.