h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Or Mostly Harmless ?

Marmalade surely requires a more expansive description than this.

Marmalade is most commonly made from 'Seville' Oranges - which are considerably more bitter than other varieties and also less juicy.

But Marmalade can be made out of other citrus fruit too, such as - Grapefruit, Lemon, Lime - or indeed a combination of these.

Other occasional ingredients include Root Ginger or Whisky.

Generally however, there is much debate about two particular qualities of the marmalade. Some like lots of chunky peel, whereas some people like thinly shredded peel or even no-peel whatsoever.
Also the overall bitterness and strength of flavour is a matter of personal preference - generally more peel would indicate more of the bitter flavours.

But marmalade is not just a simple adjunct to bread or toast. It can be used in many different culinary concoctions...
Bread and butter pudding benefits from the addition of some marmalade (although it does change the character of the pudding into "Bread-and-Butter-and-Marmalade-Pudding, because of the strength of flavour.)
Marmalade tart - a real delicacy!
Welsh cakes are very good when made with a bit of marmalade in them to give them some extra 'bite'.
Why not try adding some to a savoury dish, like chilli-con-carne or spaghetti-bolognese ? Wierd, but it works!

I've recently started having marmalade instead of pickle in my ham sandwiches. (It might work with cheese too? Hmmm...)

Also, you can glaze your lamb or pork joint with marmalade...