It's what we call a thumbtack in America. It's pretty much the same as a push pin. A drawing pin is more likely to refer to the pins with a flat disk for a head, and both thumb tacks and push pins seem to refer more frequently to the pins with the cylinder-with-a-flattened-top type pin (judging by a google image search), but basically, all three terms can refer to either form.
So. A drawing pin is a small pin or tack used to hold papers to a cork board or other flat, usually vertical surface. They are supposed to be able to be inserted without the use of a hammer, using only your thumb to push them in. They are light weight, and the point will bend easily if you attempt to insert it into too hard a surface. They always have some sort of flat, wide top, so that you can push on them without hurting your thumb.
Presumably, they were originally designed to hold papers to a drawing board, and hence the name. The history of such pins is very murky; some dictionaries have the term 'drawing pin' appearing as early as 1885, other sources say that the first pin of this form was invented by the German clockmaker Johann Kirsten in the year 1903.