Direct mail involves sending advertising materials directly to potential customers through the postal system. It has its origins in the 19th century as postal services expanded and people began sending cards and letters to advertise. Popular direct mail items included sales letters, postcards, catalogs, and brochures/folders sent en masse through the mail. Direct mail offers advantages like selectivity in targeting audiences, speed, flexibility in formats, and ability to personalize messages. However, it also faces drawbacks like higher costs than mass media and reliance on quality mailing lists.