Your workspace is your data HQ.
Everything you author lives within a workspace. It may be a personal workspace (if you're on the Core tier), or a shared organization-wide workspace (if you're on Teams or Enterprise).
Workspaces are like big "boxes" to hold all of your data, like:
Projects
Spaces
Templates
Layers
Files
Members (including your license)
Teams
Workspace Settings & Properties
You may have access to projects or data from other workspaces if it's shared with you. You may even be a member of multiple workspaces if you're collaborating with other companies.