Frankenfood is a disapproving nickname for food from genetically modified plants (and sometimes animals). People who use it want you to feel that science has built something unnatural, even a bit monstrous — not a neutral lab term. You meet it in opinion pieces, protests, and casual talk among people who distrust GM crops; food scientists and many companies avoid it because it already judges the thing it names. It is informal, journalistic, and usually uncountable in spirit (“this is frankenfood”) though you will see a frankenfood for a particular product. The joke in the name is Frankenstein: humans stitch life together and then cannot control what they made. Using the word tells people which side you are on.