The word turf originally meant the surface layer of grass and the soil held together by its roots. When you dig up a square of lawn to plant a garden, you're removing turf. Golf courses and football fields are covered in carefully maintained turf, thick and green and springy underfoot.

Over time, turf came to mean territory that someone controls or feels responsible for. A shopkeeper's turf is their store and the block around it. School hallway monitors each have their own turf to patrol. When someone says “that's my turf,” they mean it's their area of responsibility or expertise. A math teacher might joke that algebra is her turf, while the English teacher claims grammar as his.

The phrase turf war describes a conflict over who controls a particular territory or area of responsibility. Two department heads might have a turf war over which one gets to lead a new project. In history, gangs sometimes fought turf wars over neighborhoods they wanted to control.

People also use turf to mean artificial grass: the fake green carpet you see on some sports fields. While real turf grows from soil, this synthetic turf is manufactured, though it's designed to look and feel similar to natural grass.