In Achievement Hunter videos, there are several fails in which someone either "drops frames" (in other words, their capture fails), or forgets to begin recording. They often happen at bad times, in pressure situations, or have funny results.
"Dropping frames", usually referring to framerate in videos, is Achievement Hunter's term for their capture failing. Notable times include:
Jack somehow winning the first race of Things to Do in GTA V: Mario Kart, then realizing he dropped frames.
Lindsay's capture stopping due to lack of storage space after the first race of Wacky Races.
Michael's capture failing in the final Terrorist Hunt mission from Rainbow Six Vegas.