Meaning: This sentence describes a balloon as no longer being in someone's possession or unable to be found.
Choice of Words: "The" is a definite article that refers to a specific noun. "Balloon" is a noun that refers to a round, inflatable object filled with air or gas. "Was" is a verb that indicates the past tense. "Lost" is an adjective that describes something as no longer in one's possession or unable to be found.