100 episodes is considered to be the magic number at which point many television series (which usually run 22-26 episodes per year) are viable for TV syndication, usually translating to the start of the fifth season.

Many fans of story arc oriented series — rather than highly episodic ones — consider this the critical time when a show might be growing stale or starting to lose its audience, especially if it is reported to be picked up for more seasons. This can happen either because a series is changing its tone 'excessively' or sometimes not changing enough.

Series accused of the 100 episode curse include The X-Files, Angel, Buffy the Vampire Slayer, and Sailor Moon. Series such as Babylon 5 are excluded, as its fifth season is an intentional and specific ending.

There are many exceptions to the 100 episode rule — shows of fewer episodes that have become syndication successes. The most notable of these is the original Star Trek series which had only 79 episodes available when it ended in 1969. What's Happening!! did much better than in its first run on television, despite only having produced 65 episodes. An extreme example is the spy series The Prisoner which has been successfully syndicated for more than 30 years despite having only 17 episodes produced.