80-Page Giant was the name used for a series of comic books published by DC Comics beginning in 1964. The series was named for its unusually high page count. (The typical page count for American monthly comics at this time was 32 pages). The cover price was initially 25 cents, while other comics of the day were rarely above 12 cents. Many of these "Giant" issues contained reprinted material, often including material from the Golden Age era of comics. Each issue would focus upon a particular DC character or group, such as Superman, Batman, or Jimmy Olsen. The 80-Page Giant format and numbering would later be used for special extra-large, reprint-heavy issues of their regularly published titles.
In the late 1990s, DC Comics began publishing 80-Page Giant specials which were special publications relating to a series (including Secret Origins, which had not been an ongoing title for years) and which were usually compilations.
Around this time, DC was also publishing reprint-themed 80-Page Giant Annuals (also called "100 Page Spectaculars"), some of which were reprinted replicas of past Annuals and some of which were newly published reprint collections styled as the Annuals of a Silver Age title that had no Annuals during its actual run.
80-Page Giant Wikipedia