a colloid in a more solid form than a sol
"The chef added agar to turn the liquid broth into a firm gel for the dessert mold."
A semi-solid to almost solid colloid of a solid and a liquid, such as jelly, cheese or opal.
"The gel at the party was dancing all night long."
A girl.
In plain English: A gel is a soft, jelly-like substance that holds its shape but can still be squished or spread around.
"The hair gel made my hair look stiff and crunchy."
Usage: In slang contexts, "gel" is an affectionate nickname for a girl, often used to describe someone who appears cute or attractive. Outside of this informal usage, the word refers to a semi-solid substance that holds its shape but flows slowly when pressure is applied.
To apply (cosmetic) gel to (the hair, etc).
"She carefully gelled her bangs into a sleek side part before heading out for the party."
In plain English: To gel means to come together and work as a smooth, unified team.
"The mixture began to gel as it cooled in the refrigerator."
Usage: To gel something means to apply a cosmetic gel product to it, such as spreading styling gel through wet hair before shaping it. Do not use this verb to describe the physical process of a liquid turning into a solid state; for that change in texture, use the word "set" or "solidify."
Coined in the mid-19th century by Thomas Graham as a shortening of the French word for "gelatin," the term gel originally referred specifically to frozen substances. It entered English through Italian and Latin roots meaning "frost" or "to freeze."