Definition of fog index in US English:

fog index

noun

Linguistics
  • Also more fully "Gunning fog index". A measure of the readability of a piece of English-language text, expressed as the number of years of formal education thought to be needed to understand the text.

Origin

1940s; earliest use found in Journalism Quarterly. From fog + index.

Pronunciation

fog index

/ˈfɒɡ ˌɪndɛks/