A workgroup is Microsoft's terminology for a peer-to-peer Windows computer network.[1]
Microsoft operating systems in the same workgroup may allow each other access to their files, printers, or Internet connection. Members of different workgroups on the same local area network and TCP/IP network can only directly access resources in workgroups to which they are joined.
If you are not joined to a specific workgroup but your computer is in the same IP address range (for example 10.0.0.[x] OR 192.168.1.[x]) you can still access shared resources by typing the IP address or computer name, into the address bar. For example typing \\server or \\192.168.1.2. Would give you access to [server's] shared files and printers.