What's the difference between a jumper, a pullover, and a sweater?

Following on from a recent question, in Australia we have the word jumper for a knitted long-sleeved garment, typically woollen and long-sleeved.

When cosuming foreign media I always assumed the terms pullover and sweater were the names of the same garment in either Britain or America but was never clear. How much semantic overlap is there? Are any two or more terms used in the same region and if so how are they used differently? Or are is it purely down to regionalism?

I'm also interested in other words that I may have overlooked which are synonyms of any of these three in some areas or some varieties of English. In fact some posters have mentioned jersey, which I have heard many times but I'm not sure if it refers to the same garment or something a bit different.

There is a lot of regional variation on the meanings of these words. I am only familiar with US English and UK English, others can fill in the blanks:

Jumper: In the UK this just refers to an garment you wear over your shirt for warmth. It doesn't have buttons, and it pulled over your head.

In the US this has a completely different meaning. It is a type of girl's dress, a top, with attached shorts basically. (Google will be happy to show you images.) It has a kind of "little girl" sense to it kind of like pinafore, however, for sure adult women wear them too.

Sweater: In the UK this is the same as a jumper, a garment you wear over your shirt, with no buttons, and is pulled over your head.

In the US this is a similar item, however, a cardigan with buttons can also be called a sweater in the US.

Pullover: again is a garment you wear over your shirt, pulled over your head. The meaning is the same in the US and UK, but it is a pretty uncommon word in the US.

So in the UK it all means pretty much the same, however there are considerable semantic variations in the US.

This is just based on my personal observation having lived in both countries. I am sure there are lots of subtle regional variations. For example, in the UK the further north you go, the more likely you are to use jumper instead of sweater, and vice versa. Though pullover is pretty universal.

In Chile, because of the influence of many immigrants from Britain, a sweater is 'una chompa' — isn't that neat?

American usage:
Pullover is absolutely part of the wardrobe here! But it needn't be wooly — it can be made of fleece (synthetic) or a lightweight cotton-jersey knit type thing with long sleeves. Has to pull over the head versus zipping or buttoning up the front.

Sweater — any knitted thing for the top of your body. Short sleeves, long sleeves, button front, pullover, hooded, etc. You specify the details. Sweater-vest, hooded sweater, turtleneck sweater, etc.

Jumper — this is actually a dress (no shorts attached—that is a jumpsuit as clarified above) with no sleeves or collar; it is worn over a blouse or lightweight 'pullover' as we see in Catholic school uniforms here.