Vector graphics and raster images
Photographs are made up of a series of pixels or squares of different colours. These are called RASTER images. Software, such as Photoshop, is good for manipulating photos because you can edit individual pixels. However, because raster images are made up of individual pixels they do not scale very well. This is especially problematic for text, which can appear fuzzy and pixelated.
For text and graphics it is better to use a programme designed for vector graphics, such as Illustrator. Rather than storing information about individual pixels, vector graphics store information about how to draw the image. This means that these types of graphics maintain their resolution when scaled and work well for text and solid shapes.