noun

• (informal) An error; a mistake in the performance of an action.
  "1962 November 6, Richard Nixon, “Gentlemen, this is my last press conference”, 2008, Rick Perlstein (editor), Richard Nixon: Speeches, Writings, Documents, page 111, I made a talk on television, a talk in which I made a flub—one of the few that I make, not because I′m so good on television but because I′ve been doing it a long time. I made a flub in which I said I was running for governor of the United States."
• (slang) A fold of fat.

verb

• (transitive) To goof, fumble, or err in the performance of an action.
  "‘Stage fright? So? What are you babbling ′bout? You′re mad as a snake!’ ‘Ever since I was a kid. I was in the Christmas Pageant one year and flubbed my line.’ ‘What was your line?’ ‘I told you I flubbed it!’ he mouthed these words hysterically."