The Greek noun borboros (G1004) refers to mud, mire, or filth — particularly the dirty, foul mud in which pigs wallow. It appears once in the New Testament, in 2 Peter 2:22, as part of a proverb about the sow returning to wallow in the mire.
Peter uses borboros as part of a devastating double proverb about false teachers and apostates: "The dog returns to its vomit" (from Proverbs 26:11) and "The sow, after washing herself, returns to wallow in the mire." The image is stark — those who know the truth and then return to their former corruption are compared to animals returning to their natural filth. This is a sobering warning about the danger of superficial conversion.