bitmap-raster-image

Raster (or bitmap) images are fixed-resolution, made of a grid of pixels. Enlarged they will be blurry and pixelated, with a jagged edge.
Common raster file formats are jpg, gif, tiff, bmp and png.

Vector images can be enlarged to any size with no loss of resolution—they are created using a mathematical formula that determines the curve/vector between points.
A pure vector file format is svg (scalable vector graphic). Adobe Illustrator files are typically vector, but Illustrator also supports placed raster images, just as Adobe Photoshop files support vector layers. Pdf and eps files also support both vector and raster images, so asking for an Illustrator, pdf or eps file does not guarantee that you’ll end up with vectors. If you need vectors, ask for a vector file. Vectors may be delivered as an eps, pdf, or ai file, but an svg file will always be a vector.

vector-scalable-image

Your logo should be in a vector format so that it can be reproduced at any size. Ask your designer for a vector pdf with type converted to paths to guarantee excellent reproduction at any size.