If you have been advised that there may be rasterised fonts in your artwork, this means that some or all of the text in your artwork is made up of pixels rather than vectors.
When creating text in desktop publishing software (e.g. Microsoft Publisher / Adobe InDesign), or vector software (e.g. Adobe Illustrator / Corel Draw), the text is made up of shapes which can be scaled indefinitely without losing quality. However, if a design is saved to an image file format (e.g. JPEG / Tiff), the text automatically becomes rasterised (it is no longer made up of vector shapes, it is now made up of pixels). This means that if you enlarge text it will lose quality.
High resolution rasterised text may look the same as vector text when printed. However if rasterised text is low-resolution it may appear blurry, jagged or pixelated. If the rasterised text is very low resolution it may appear so blurry and pixelated that it is no longer legible.