Transformer/Adaptor--what's the difference?

I've been reading alot to figure out the electronic thing, and every time I think I understand, I read something that confuses me more.

Latest question: what's the difference between a transformer and an adaptor? (This came up in the laptop thread).

Thank you!

Adaptor allows you to use a UK plug in a US outlet or any other country's plug in another country's outlet.

Transformer actually changes the voltage so that you can use a US appliance in another country like the UK.

Very brief and not technical at all summary but hope that helps.

You can use an adapter IF your US appliance is rated 110-240 volts.  If it is 110-120 you will need a transformer or converter

You need to be a little careful with the term though.   Adapter can cover a broad range of things, and while it's often used to mean simply a plug adapter (which allows two otherwise incompatible connectors to be mated together, without changing the voltage), it is sometimes applied to transformers or other converters which do change the voltage or other power characteristics.

Look at the units which are commonly supplied with printers, laptops, and similar equipment.  They are sometimes referred to as power adapters, since they adapt the type of power (from 120 or 240V A.C. to a lower voltage A.C. or D.C.).    It's a very broad term which can mean different things. 

It's not at all unusual to find some plug adapters marketed as converters too, even though they are just performing the basic mechanical adaptation of the plugs & receptacles, without changing the power characteristics in any way.

What great responses! Thank you--the electricity-demystification process begins.