Girl Friday

Girl Friday is the antiquated name for an office/personal assistant. Duties for these minions of executives include but are not limited to:

Dictation
Typing
Filing
Accounting
Answering Phones
Faxing
Making Appointments
Breaking Appointments
Showing Boss Where the 'Enter' key is on Keyboard
Retyping the Document He Was Working On
Cleaning Office Kitchen
Making Coffee
Making It Again When You Use Mocha Java Instead of Hazelnut
Ordering Lunch
Picking Up Drycleaning
Getting Photos Developed
Babysitting Boss's Kids
Getting Boss's Range Rover and Jaguar and Mercedes Washed
Giving the Other Driver $100 to 'Just Forget About This Little Fender Bender'
Polishing Awards
Glueing Award You Dropped While Twirling It Like a Majorette
Enduring Screaming Boss
Getting Fired

The origin of the phrase comes from Daniel Defoe's novel Robinson Crusoe:

In a little time I began to speak to him, and teach him to speak to me; and, first, I made him know his name should be Friday, which was the day I saved his life.

The character Friday in Crusoe is a man--a savage that Robinson encounters on an isolated island. However, Friday becomes a faithful assistant and becomes invaluable to Robinson.

Nowadays, a Girl (or Guy) Friday is an all-around office helper. However, the phrase can apply to anyone who is skillfully versatile and dependent in many tasks.