Dictionary.net

This term in its most extended sense includes all contributions imposed by the government upon individuals for the service of the state, by whatever name they are called or known, whether by the name of tribute, tithe, talliage, impost, duty, gabel, custom, subsidy, aid, supply, excise, or other name.

The 8th section of art. 1, Const. U. S. provides, that "congress shall have power to lay and collect taxes, duties, imposts, and excises, to pay," &c. "But all duties, imposts and excises shall be uniform throughout the United States."

In the sense above mentioned, taxes are usually divided into two great classes, those which are direct, and those which are indirect. Under the former denomination are included taxes on land or real property, and under the latter taxes on articles of consumption. 5 Wheat. R. 317.

Congress have plenary power over every species of taxable property, except exports. But there are two rules prescribed for their government, the rule of uniformity and the rule of apportionment. Three kinds of taxes, namely, duties, imposts and excises are to be laid by the first rule; and capitation and other direct taxes, by the second rule. Should there be any other species of taxes, not direct, and not included within the words duties, imposts or customs, they might be laid by the rule of uniformity or not, as congress should think proper and reasonable. Id.

The word taxes is, in a more confined sense, sometimes applied in contradistinction to duties, imposts and excises. Vide, generally, Story on the Const. c. 14; 1 Kent, Com. 254; 8 Dall. 171; 1 Tuck. Black. App. 232; 1 Black. Com. 308; The Federalist, No. 21, 36; Woodf. Landl. and Ten. 197, 254.