South East Asia haze: What is slash-and-burn?

There has been concern over the extent of land clearance for palm oil plantations in Indonesia

Singapore and parts of Malaysia and Indonesia have been shrouded in a dense, pungent smog in recent days caused by fires in Indonesia.

Pollution levels have hit record highs and while the blame game goes on, the one common factor has been the term "slash-and-burn".

What is slash-and-burn?

Why do they use slash-and-burn?

The growing demand for palm oil has made the crop a lucrative farming option

What are they clearing the land for?

So, how much land is being cleared for palm oil plantations?

If slash-and-burn is illegal, why isn't it being stopped?

So who is responsible?