This is perhaps the biggest of the many questions we ask: 'What is Life?'
Of course, no one has the answer, it's all just guesswork.
Perhaps by starting at the opposite end we can find clarity. So, what is death?
We can't really understand life without thinking about death, or the absence of physical movement and self-expression.
Now this may sound a bit morbid but I had a bit of a eureka moment when I realised that life and death stand together at the same door.
These two, life and death, actually are the door - entry into and exit from, our physical incarnation. They are twins who cannot survive without the other.