In this sentence, "gibber" refers to the nonsensical sounds a baby makes, often before they can speak properly.
Here are a few other ways to use "gibber" in a sentence:
* "The drunkard's gibber was unintelligible, even to his closest friends."
* "The professor's lecture was filled with so much gibber that the students couldn't make sense of it."
* "The old woman's gibber was a mixture of English and her native tongue."
Remember, "gibber" is often used to describe speech that is nonsensical or difficult to understand.