Many people have tried to pin-point the precise definition of what improvisation is, but defining improvisation can be as unique as an individual playing improvisation because it is forever changing. Here are a few of the limitless ideas that describe improvisation:
…Telling a story with music
…Expressing emotion
…Playing music that incorporates a known melody with musical decorations
…Musical expressions of the soul
There are an infinite number of explanations, but most importantly: What is improvisation to you? Knowing this answer will help you greatly in developing your solo style.
From a technical standpoint, improvisation uses notes, rhythm, and silence to express musical ideas in infinite musical combinations. From a auditory perspective, each time a person improvises a solo, it is never the same way twice.