A double hammock is made to support two people and is usually rated to safely hold at least 400 pounds. Two people can share a double hammock, but it’s usually pretty uncomfortable to actually sleep together with another person in a hammock.
Many single users prefer double hammocks. The extra material offers additional space to spread out, and some sleepers like to wrap the hammock’s material around them like a cocoon. Double hammocks are generally heavier, but they offer some nice comfort that you may find is worth the weight.