Sidenotes are a form of annotation used in textual works, placed alongside the main text, typically in the margins of a page or a digital screen. They serve to provide additional information, context, or references without interrupting the flow of the primary content. Unlike footnotes or endnotes, which are located at the bottom of a page or the end of a document, sidenotes are conveniently positioned close to the related text, making it easier for readers to access supplementary details or insights without losing their place in the main body of text.

In digital formats, sidenotes can be particularly dynamic, offering interactive elements like hyperlinks, embedded images or video, or collapsible text sections. They enhance reader engagement and understanding by allowing for immediate access to extra information, clarification, or authorial commentary. This feature is especially useful in academic, technical, and literary works, where additional context or explanations can significantly aid in comprehension. The design and integration of sidenotes require careful consideration to ensure they are informative without being distracting, maintaining a balance between the main content and the supplementary annotations.