The open command lets you open a file using this syntax:

open <filename>

You can also open a directory, which on macOS opens the Finder app with the current directory open:

open <directory name>

I use it all the time to open the current directory:

open .

The special . symbol points to the current directory, as .. points to the parent directory

The same command can also be be used to run an application:

open <application name>

The open command works on macOS only. Use xdg-open on Linux