Chonies is a colloquial expression, used for underwear in general.
It may refer to panties, as well as boxers, if used in English, although in Spanish, it is used informatively by women only, as with men it carries a belittling connotation.
Although “Chonies” is a slang expression used both in English and Spanish, it is not used outside the US and Mexico.
The term “Chonies” is a slang derivate of the Spanish word Calzones, which translates to breeches or trousers, though there is an extremely delicious Italian dish with the same name.
The large Spanish-speaking population of America has led to the adoption of “Chonies” and it may be used in American English too, although it is still mostly prevalent in areas of the US, with a significant Hispanic population.
Today, the word is especially used in the context school, like in the changing room, when kids are laughing at the soiled “Chonies” of an unlucky classmate.
Urban Dictionary added the term to its list of definitions in 2003, with several other entries and interpretations published on the site since then.
“Chonies” is mostly prevalent in the southern states of the US, and the norther one goes, the less likely they are to encounter it.
“Chonies” was also adopted as the nickname of a character from the Netflix series, titled Dogs in Space.
Although it is especially popular among the younger generations, the slang term is also used by other across the United States. Due to its close assonance with the word Chode, “Chonies” is a likely slang term for underwear and other articles of clothing, related to the crotch area.