Bitmaps (also referred to as raster) files use pixels (bit) on a fixed grid (map) to define an image. A bitmap image is made up of millions of tiny dots called pixels, where each pixel represents a different colour.
Because a bitmap uses pixels and each pixel has unique colour and location information, bitmap files are generally:
Most of the images on the internet are raster files, which have been saved down to the standard web resolution: 72dpi. These files are poor choices to use in print.
If you are looking for high quality images at 300dpi, the best place to start are on stock photo websites.
Common uses for raster images include: flyers, booklets or catalogues, brochures or pamphlets, posters, etc.
Vector graphics use points and curves
(or paths) and a formula to create an image. With vector graphics you can edit each object separately, change the size, position, shape or colour.
Because a vector graphic uses a formula to calculate the fill, colour and stroke (and not pixels) files are:
Company logos and illustrations will always produce better results as vector graphics. Type / fonts can also be converted to vector format, which makes them great when scaled to really large sizes.
There are plenty of websites offering high quality vector or illustrations online with free or paid options. Vectors are a flexible option since they can be used for both print and web.