The Happy Gland is an emotion that causes happiness. It is shown in the episode "Fresh Breath of Squidward." It is also unknown whether or not the Happy Gland is actually real.
The Happy Gland is the same color as Squidward and has the same eyes as him as well, this is due to the gland being inside Squidward's head.
The Happy Gland appears in the episode "Fresh Breath of Squidward" when Squidward explains to SpongeBob and Patrick that whenever he sees them, a storm cloud forms over his happy gland. The Happy Gland attempts to shelter itself from the storm with an umbrella, but the winds blow the umbrella out of its hand, causing the gland to get the flu.