[quietbritishjim]

> sugar is glucose + fructose.

That's not the definition of sugar. Not even if you meant sucrose there (which is different from just a mix of glucose and fructose). Wikipedia puts it:

> Sugar is the generic name for sweet-tasting, soluble carbohydrates, many of which are used in food. ... White sugar is a refined form of sucrose.

I know Wikipedia is not perfect but that matches what I've seen in the past. For example, fructose (by itself) is absolutely a sugar and it would be outrageous to claim it's not because it's not sucrose.

[infinite8s]

You are correct that that is not the scientific definition of sugar, which is generally any 5 or 6 carbon ring molecule.

However when most people talk about sugar they are referring to table sugar, which is a molecule of glucose (a six carbon ring sugar) chemically bonded to a molecule of fructose (a 5-carbon ring sugar) - otherwise known as sucrose. The first thing your body does when it sees sucrose is split them into a molecule of glucose and a molecule of fructose (this happens in your small intestine). Glucose can be metabolized right away, in any cell, however fructose needs a bit more processing in the liver before cells can use it to generate ATP.

[quietbritishjim]

> ... when most people talk about sugar they are referring to table sugar ...

What can I say? (shrug) I disagree, that's not my experience from talking to people in person (about diet; obviously it's a different matter if you're talking about cake ingredients). Anecdotal evidence from replies here on HN seems to agree with you though. Who knows what's more common in reality.