Combo box vs. Drop down list box

The Drop down list box is often, incorrectly, called a Combo box.

It does not sound like a big issue but user interface wise it is.  A Drop down listbox only takes existing values as a Combo box allows entering of new, unknown, values.  When talking about Combo boxes don't forget to clarify what should happen if the user enters a value that doesn't exist in the list.

Like this:
"We would like to select the Customer from a Combo box."
"What should happen if the user enters the name of a Customer that doesn't exist?"
"The Customer should be created."
"Where from?"