Meaning of MAC terminal command prompt
That line is called command prompt.

dhcp-74-148 is you hostname that you received from dhcp server.

~ is where you currently are (which directory) - tilda means you are in your home folder, /Users/[username]

: just separates hostname from current directory.

You can change format of command prompt by changing $PS1 variable.
And - if you're interested - check out some bash shell tutorial for more information.