A term describing a period beginning in the mid-1950s when superheroes made a successful comeback in comic books.
Nearly everyone agrees that the Silver Age began with the publication of DC Comics' "Showcase #4", which introduced the new and improved Flash. Other early milestones included the new and improved Green Lantern, the first appearance of the Challengers of the Unknown, the introduction of the Justice League of America, and the first appearance of the Fantastic Four.
Silver Age comics were noted for much improved art and more recognition for comics creators, as they were nearly always credited for the stories they created (unlike the Golden Age when many creators toiled in relative anonymity). Both DC and Marvel enjoyed strong success, with Marvel in particular benefiting from appreciation of the comics of Lee, Kirby, and Ditko by college students and the counterculture. The Silver Age also saw a rise in the popularity of underground comix.
The end of the Silver Age is much disputed. Many mark the end of the Silver Age as being the publication of "The Amazing Spider-Man #121" in June 1973, better known as "The Night Gwen Stacy Died." Others have it pegged to Jack Kirby leaving Marvel to work for DC in 1970. Others pick different creators leaving comics they'd been closely associated with during the Silver Age. Others just pick the end of the 1960s as the time when the Silver Age transitioned to the Bronze Age.