Grit is a term popularized by Angela Duckworth to mean "perseverance and passion for long-term goals" "despite experiences with failure and adversity". It's what differentiates high achievers from the rest of us. Dr. Duckworth viewed Grit as a personality trait and her research "concluded that Grit is a better predictor of success than intellectual talent (IQ)". However, Grit as a separate personality trait is not without its critics.
A 2016 meta-analysis concluded that “that Grit as currently measured is simply a repackaging of Conscientiousness”. In a brand new study from a different research team, the researchers found that Grit shared 95% of its variance with Conscientiousness (one of the big five personality traits).
What this means is that Grit and Conscientiousness are tapping into the same thing. The authors of this study concluded that "the findings suggest that proponents of Grit are falling for the jangle fallacy – mistakenly believing they are measuring something different because they have given a new name to an existing concept".
"Schmidt and his team concluded that perseverance, the facet of Grit that has received most attention because of its links with success and achievement, is a redundant concept. It is really just another word for industriousness, which is already a well-researched and recognised aspect of the pro-active side of Conscientiousness."
Schmidt, F.T.C., Nagy, G., Fleckenstein, J., Möller, J., & Retelsdorf, J. (2018). Same Same, but Different? Relations Between Facets of Conscientiousness and Grit. European Journal of Personality, 32, 705-720. https://doi.org/10.1002/per.2171