No-vig probability
A no-vig probability is a market price with the sportsbook margin mathematically removed, so the two sides sum to 100 percent.
In plain English
Stripping the vig gives a cleaner read of what the market actually thinks, which is why it is the usual basis for comparing a market price against an opinion or against another book.
Example
Two sides at -110 each imply 104.8 percent together. Removing the margin proportionally puts each at about 50 percent.
Why it matters
Comparing your view against a raw price rather than a no-vig price makes every market look worse than it is, and can hide genuine differences.