Wilhelmina's Broom (or simply Broom) is the name of a sentient broom companion and vehicle of Wilhelmina Witch. Willie uses male pronouns to refer to him. He is the focus of Where-Helmina's My Broom?!
She's had him since she was a baby (Dorothy referred to him as "your Toto") and it is able to move independently, unlike the broom used by Willie's aunt (Wicked Witch of the West) which she was unable to fly on when she lost her magic powers.
Initially Willie is resistance to acknowledging him as a friend (just calling him "my ride") but eventually laments he IS her friend, and later emphasizes BEST friend.