The SMB protocol (Server Message Block) is used for providing shared access to files and printers.
Historically, SMB ran on top of NetBIOS over TCP/IP using port 139.
SMB can also run directly over TCP/IP without the NetBIOS layer, which uses port 445.
Therefore, TCP port 445 is used to provide the SMB protocol without NetBIOS.
Reference:
Official IANA port numbers: https://www.iana.org/assignments/service-names-portnumbers/service-names-port-numbers.xhtml
Microsoft documentation on SMB: https://docs.microsoft.com/enus/windows/win32/fileio/microsoft-smb-protocol-and-cifs-protocol-overview
