Commands placed between parentheses are executed in a new child shell process rather than the shell process that received the commands as input.

This can be useful if you want a command to run in a different directory or with other alterations to its environment, without affecting the current shell process.

shell-prompt: (cd /etc; ls)
        

Since the commands above are executed in a new shell process, the shell process that printed "shell-prompt: " will not have its current working directory changed. This command has the same net effect as the following:

shell-prompt: pushd /etc
shell-prompt: ls
shell-prompt: popd