Sheridan is a temperate planet, located out on the fringes of Stellar Federation territory.
It's essentially the Pearl Harbour of the Galaxy, as it lies on the boundary between the Stellar Federation's territory and that of the Midori Empire. Unfortunately, this means that Sheridan's planetary defense base is frequently subject to invasion whenever Princess Midori choose to venture outside the realms of her Empire.
According to series creator Craig Black, this planet is named for the late voice actress Susan Sheridan, of Noddy and The Black Cauldron fame. This also accounts for Captain Hawkins, named for Peter Hawkins, a fellow voice actor, frequent collaborator with Sheridan, and the originator of the voice for Doctor Who's Daleks.