a preserve made of the jelled juice of fruit
"She spread a thick layer of strawberry jelly on her toast for breakfast."
any substance having the consistency of jelly or gelatin
"The thick, translucent substance that formed on top of the fruit punch was just a layer of natural jelly."
A dessert made by boiling gelatine, sugar and some flavouring (often derived from fruit) and allowing it to set, known as "jello" in North America.
"After the pot boiled down, she poured the mixture into a mold to make sweet jelly for dinner."
In plain English: Jelly is a sweet, wobbly dessert made from fruit juice and sugar that has been set with gelatin or pectin to give it its firm texture.
"She poured some strawberry jelly on her toast for breakfast."
Usage: Use this word to describe the firm, wobbly sweet dish served with whipped cream or strawberries rather than a soft spreadable substance like jam. Be aware that American English often prefers the brand name Jell-O for this specific dessert.
To wiggle like jelly.
"The toddler wobbled so much that he seemed to be jiggling like jelly."
Jealous.
"After seeing his friend get promoted, he became absolutely jelly about not receiving any recognition."
The word jelly comes directly from Middle English gele, which was borrowed earlier from Old French and Latin to describe a gelatinous substance. It entered modern usage as the standard spelling for this food item, while its doublet jelly also exists in some dialects but is less common today.