Sheep is a domesticated ruminant mammal with a thick woolly coat and (typically only in the male) curving horns.
In slang, calling someone a "sheep" means they are meek, timid, or easily led.
The term "sheep" also refers to:
1. A person who is too easily influenced or led
2. In computing, a "sheep" is a process that follows another without thinking
3. In Christianity, Jesus is often referred to as the "Good Shepherd" and his followers as his "sheep"