More robust:

  open -b com.Microsoft.Excel

That will open it even if it has a different name or is in a different directory.

Disadvantage: autocomplete doesn’t work on that in the terminal.

Hmmm:

    The files /Applications/Microsoft and /Users/lsllc/Excel.app do not exist.

Missing a backslash! [0] ... how quaintly Microsoft!

/s

[0] To escape the space, or you could quote the entire argument to `open`