What do you think time is?

They say time is a thief, taking everything you hold dear. Some say time brings life. Others say it's a circular cycle, never stopping. Others argue that time is linear. Some say history can be changed with a little bit of power and determination while others say it is solid. Some believe the future to be fluid, ever-changing but they also say that fate cannot be changed.
Tell me, what is it do you think the reality..... Or illusion we live in to be?