TL;DR FRI is a protocol that demonstrates proximity for a linear code to a low-degree polynomial. FRI is a round-by-round interactive protocol between a prover and a verifier. The prover commits to a Reed-Solomon codeword that evaluates to some low-degree polynomial. The verifier makes oracle queries to the alleged codeword at random points and verifies that the result matches the given commitment. If sufficient queries succeed, the verifier is convinced that the committed codeword will pass the low-degree test. Overview FRI - Fast Reed-Solomon IOP of Proximity is a low degree test that allows a Prover committing to a low-degree polynomial demonstrating to a Verifier that the polynomial has a bounded degree $d$, without revealing the polynomial. More specifically, the FRI protocol shows an alleged codeword being close to a low-degree polynomial $h(x)$ without revealing the entire codeword itself. The values in the codeword are evaluations of $h(x)$ over a fixed size domain $\Omega\subseteq \mathbb{F}$; $\Omega$ is a multiplicative subgroup of a finite field $\mathbb{F_p}$, of order $p$. The degree of the polynomial lasts below a certain threshold $d$.