Have you ever wondered what exactly distinguishes a jam from a jelly? If both were put on a spoon and taste-tested by 100 different people, the identifying results would probably turn out to be a jumbled, coagulated mess. So if it isn’t the consistency, color, or flavor that makes a jam stand apart from a jelly, what is it?
The difference is in the manufacturing process. Jelly is made from the juice of a fruit by crushing said fruit, and then straining out the larger chunks. The liquid is then brought to a boil, and add additional sugar and pectin, a natural thickening agent, are tossed in the mix. The resulting viscous liquid is jelly.
Now for jam: Just take the entire process listed above verbatim, then remove the phrase “and then straining out the larger chunks.” Jam is just jelly sans-straining.
Next up, preserves and marmalade. Preserves and jam are very similar, due to the fact that both forego the straining process. However, preserves have much larger chunks of fruit. And marmalade distinguishes itself from regular old preserves not through processing, but through ingredients; marmalade is just preserves made from citrus fruits.
(If you have a craving for preserves, jam, jelly, or marmalade now, make sure you make the best possible toast to go with it!)
Source: Mental Floss