Glee
A full list of special holiday episodes

A musical dramedy about a high school glee club and their journey to national fame, tackling social issues and personal struggles along the way.
The show aired 4 Christmas episodes, 1 Thanksgiving episode, 1 Halloween episode, and 3 Valentine's Day episodes.
Christmas episodes:

Season 2, Episode 10
A Very Glee Christmas
Finn attempts to spread holiday cheer at McKinley High while Sue dons a Grinch disguise to steal Christmas presents.

Season 3, Episode 9
Extraordinary Merry Christmas
The Glee Club faces a tough choice when they are invited to perform at two conflicting events happening at the same time.

Season 4, Episode 10
Glee, Actually
Sam and Brittany enjoy their final days before the predicted Mayan apocalypse, while Kurt has a memorable Christmas.

Season 5, Episode 8
Previously Unaired Christmas
New Directions audition for roles in McKinley's living Nativity Scene while Rachel, Kurt, and Santana work as Santa's elves at a mall in New York. The episode was not allowed to air by FOX the previous year.
Thanksgiving episodes:

Season 4, Episode 8
Thanksgiving
Some McKinley alumni offer New Directions advice on their Sectionals performance while Rachel and Kurt have an unconventional Thanksgiving dinner.
Halloween episodes:

Season 2, Episode 5
The Rocky Horror Glee Show
Will, consumed by jealousy, decides to produce a controversial school play - "The Rocky Horror Picture Show" - and Sue supports him for her own devious reasons.
St. Valentine's Day episodes:

Season 2, Episode 12
Silly Love Songs
The glee club's Valentine's Day kissing booth ends up causing heartbreak and disappointment when things don't go as planned.

Season 3, Episode 13
Heart
Will challenges the Glee Club to find and perform the world's greatest love songs in honor of Valentine's Day.

Season 4, Episode 14
I Do
On Valentine's Day, Will and Emma get married in Lima, and their union brings together both past and present members of New Directions to celebrate.