Junk mail refers to unsolicited, unwanted, or irrelevant mail that is sent to individuals or businesses. Junk mail can take many forms, including advertisements, flyers, catalogs, or promotional materials. It is typically sent in mass quantities and is often considered a nuisance by recipients who do not find the content relevant or valuable. Junk mail can clog up mailboxes and waste resources, leading many people to seek ways to reduce the amount of junk mail they receive, such as opting out of mailing lists or using filters to block unwanted mail.

In contrast to intelligent direct mail, which is targeted to a specific audience and aims to generate sales or leads, junk mail is indiscriminate and aims only to get the recipient's attention. Technology and data analytics have made it easier for companies to send targeted and relevant direct mail campaigns, which can help reduce the perception of direct mail as junk mail.