Most dot matrix printers have a print buffer, a special chunk of memory for temporary storage. When you print a document, the computer sends out the necessary information faster than the printer can print it. If the printer has a buffer, the information the printer can't deal with immediately goes into the buffer, where it waits until the printer is ready for it. As soon as the entire document is in the buffer, you can use your computer again for other work, while the printer takes its time to print the "buffered" information. The larger the print buffer, the more it can hold and the faster you get your screen back.
Print buffers are similar in concept to print spoolers, but a spooler works by parking the extra information to be printed on your hard disk, rather than inside the printer.
Laser printers have memory, but there's no separate section set aside as a buffer-any memory not used for the page currently being printed (or for fonts), is available for temporary storage.