A workspace is a common space where team members can cooperate, monitor their activities and work together.
When you join a workspace, you’ll create an account using your email address. You can use the same email address to join as many workspaces as you’d like, but you’ll have separate Slack accounts for each one.
Within a workspace you can also create different Teams, so that it's easier to split the members of an organizations accordingly. For example, if an organization has both a Support and a Sales Team, a best practice would be to include them all within the same workspace, but split the teams accordingly in two different entities.