For starters, Procrastination comes from a Latin word Procrastinare which means belonging to tomorrow.
In short to put off until tomorrow. It is when we delay the important tasks we need to do. Either by taking up tasks that are not that important or urgent or by ignoring it till the last minute.
We would rather clean our whole room, do the dishes, organize our closet than do that one important assignment or presentation that you have to submit tomorrow morning. This is because we dread doing the task, so we replace it to feel better. But it is only temporary, we eventually have to face the reality and get it done.