Bitmap VS. Vector Images
Bitmap images use pixels to create images. (Photoshop creates and edits pixels)
As a bitmap image is enlarged the image becomes jagged and blocky as the pixels become more pronounced and defined.
This is why we want high resolution (300 pixels per inch) images for print projects like the Yearbook.

Vector Images use mathematical formulas to describe the arcs and curves. (Illustrator is a vector design app.)
As Vector images are enlarged there is no loss of quality as lines continue to be smooth.