Final answer:
A theme is a pre-designed set of visual elements including colors and fonts that can be applied to a document to ensure professional and consistent appearance.
Step-by-step explanation:
A theme is a built-in combination of colors and fonts. When you apply a theme to a document in software like Microsoft Word, it changes the overall look of the document with cohesive color schemes and font styles. This helps in maintaining a professional and visually appealing consistency throughout the document. For example, if you select a 'Modern' theme, it will apply a specific set of fonts and colors designed to give a current and sleek appearance to your work.