It is such an abstract concept that it can have a number of descriptions. Some people think of an “Aha!” moment. Something seemingly brilliant comes out of the blue. A lightbulb goes on. One is lifted up in mood by a magic blend of brain and emotion which rises suddenly to consciousness.
The Oxford Dictionary (http://www.oxforddictionaries.com/definition/english/inspiration) defines it as
“1 [MASS NOUN] The process of being mentally stimulated to do or feel something, especially to do something creative”
I believe inspiration is more than just mental stimulation. My most apt definition would be “Inspiration is a holistic state of heightened creativity arising from a blend of childhood wonder and an enlivened spiritual resonance.”
Creative people have always discussed inspiration; what it is; how it feels; how to get it; how to kickstart your work with it; whether you should wait for it before creating. It is as well known as it is just as well unknown. Probably, it is a bit different for as many different people. I think of it as something that at first comes slowly like a shadow from a creaking door, then it springs into bloom and you feverishly write or paint or build. You work from that Zen-like flow state. You can feel it as though you are channeling something from where you don’t know, but it is coursing through your being. You also feel it has a life of its own: it starts when it wants to, carries you along for minutes or hours, and in a moment of calm you recognize it is coming to a distinct sense of conclusion by coming to a close, the way a story does. Either way you know it has finished its message and it is now up to you to carry on through the remainder of the work. You neither know when inspiration will return, nor do you care. You are simply open to its return, and you are willing to do the hard lifting when it floats away.