Raised, in this sense, means higher than the ground or surface around it. A raised platform is a floor built up so you stand above the room. Raised letters on a sign stick out so you can feel them. A raised bed in a garden is a box of soil higher than the path. It is a normal, slightly careful word; you meet it on signs, in instructions, and in descriptions of rooms and streets. Though actually, English uses raised in neighbouring ways that are not this physical sense: a raised voice is louder, not sitting higher, and a raised eyebrow is a face moving up. Here the thing itself is built or set up above what is next to it.