Virtually any popular TV show is a fad, since they all fade away eventually -- if they're not outright cancelled. Several 1990s TV shows really defined the decade, though. You can't talk about the trends of the time without acknowledging the enormous influence these shows had on the kids coming up at the time -- especially since the decade offered more opportunity to see themselves on screen than ever before.
"Beverly Hills 90210" was a soap opera about affluent teens at a posh California high school. It debuted in 1990 and its 10-season run perfectly bookended the decade. Ask anyone who grew up in the '90s who Brenda and Dylan were and you'll surely get a passionate reply. The show dealt with topical issues like drug use, teen suicide and abortion, but its breezy peek into the lives of privileged teens gave way to shows like "Gossip Girl" and "The O.C."
"Saved by the Bell" was "Beverly Hills 90210's" little sister. While the shows are unrelated, "Saved by the Bell" covered similar themes, but was aimed at a younger audience. The cast members are perhaps better known for their post-Bell exploits than for the merits of the show itself, and certain infamous moments (like Jessie Spano's amphetamine freakout) have become YouTube classics.
While "Buffy the Vampire Slayer's" run extended beyond the '90s, it debuted in 1997, and the first seasons are its finest. It perfectly exemplifies another '90s trend: girl power. The heroine of the show is a high school student gifted with superpowers she must use to fight vampires and demons. The popularity of supernatural teen drama, manifested today in the "Harry Potter" and "Twilight" series, can be traced back to "Buffy."