partial derivative

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The derivative with respect to a single variable of a function of two or more variables, regarding other variables as constants.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun mathematics A derivative with respect to one variable of a function of several variables.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the derivative of a function of two or more variables with respect to a single variable while the other variables are considered to be constant