Definition: fruit (or other soft ingredients) blended smooth, used as a topping, filling, flavouring or sauce.
A purée (pyoo-ray) is just something blended until smooth — but a few small things make it behave. For a fruit topping like the mango on our cheesecake, drain tinned fruit really well before blending, or the extra liquid slackens it and it runs off the top. Fresh fruit purées are usually sharper and looser than tinned; a little icing sugar balances a tart one, and a brief simmer will thicken a runny one if you need it to hold.
In practice: drain well before blending for a topping — wetness is the enemy of a purée that sits neatly.