A hindrance is something in the way, an obstacle. An untied shoelace is a hindrance to walking, and tripping in the lunchroom might be a hindrance to getting a seat at the cool table.
You might hear the phrase, "more of a hindrance than a help." It means that something intended to be a positive force has the opposite effect, like when your four-year-old sister tries to help you make dinner. Hindrance refers to the act of slowing things down, or the thing that's causing the problem, like your "helpful" little sister. It's the noun form of the verb hinder, which is "to get in the way."