Footnotes are notes placed at the bottom of a page in a book or document that provide additional information or references related to the text. They help clarify points, offer citations, or give extra context without interrupting the flow of the main content. Typically indicated by a small number or symbol in the text, footnotes allow readers to explore topics like historical events, research studies, or definitions without cluttering the main narrative. They are commonly used in academic writing, where precise sourcing is essential for credibility and thoroughness.