Faltering is the action of hesitating or losing strength. A game show contestant's faltering might cause her opponent to win.
Use faltering as a noun to mean the act of wavering or pausing uncertainly, or as an adjective: "My faltering answer did not impress the history professor." Faltering progress on your neighbor's house addition might make you wonder if it'll ever be finished, and a faltering career is one that's not improving or earning more money. The verb falter comes either from a Scandinavian root, or possibly the Middle English falden, "to fold."