Sheep is the general word for the animal in question. A ram is a male sheep and a ewe is a female sheep, while a lamb is a baby sheep. You probably already know that sheep doesn't change in the plural (1 sheep, 2 sheep, 3 sheep, etc), while the other three words add -s in the plural.

Hi Ana, Sheep is the name of a species. You can have male and female sheep. But, a ewe is the name for a female sheep and a ram is the name for a male sheep.