empirical formula

from The American Heritage® Dictionary of the English Language, 4th Edition

• n. A chemical formula that indicates the relative proportions of the elements in a molecule rather than the actual number of atoms of the elements.

from Wiktionary, Creative Commons Attribution/Share-Alike License

• n. A notation indicating the ratios of the various elements present in a compound, without regard to the actual numbers.

from the GNU version of the Collaborative International Dictionary of English

• adj. See under Formula.
• n. an expression which gives the simple proportion of the constituents.

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

• n. a chemical formula showing the ratio of elements in a compound rather than the total number of atoms