Cells are the fundamental units within a spreadsheet, such as Microsoft Excel or Google Sheets. They are the individual rectangular boxes formed by the intersection of rows and columns in the grid-like structure. Cells serve as containers to hold and organize data, allowing users to input, manipulate, and analyze information. Each cell is uniquely identified by a combination of a letter and a number, denoting its column and row position. Cells can store various types of data, including text, numbers, dates, formulas, and functions. They enable efficient data management, calculations, and presentation in a tabular format.