These are technically called _infantry of the line_, and _cavalry of the line_.

In this sense of the term, light infantry, light cavalry or dragoons, artillery, and engineers, are not classed as troops of the _line_.

But this distinction is now pretty much fallen into disuse, and the division of an army into Staff and Administrative departments, and four arms of service--Infantry, Cavalry, Artillery, and Engineers--is now regarded as the most convenient, from being precise and definite in its meaning.
The _general staff_ of an army includes all general officers of the army, and such officers of lower grades as are attached to this general duty, instead of serving with troops, or on special administrative duty.
The general officers are--1st, the _generalissimo_, or commander-in -chief; 2d, _generals_, or marshals, as they are called in France, or field-marshals and generals of infantry and cavalry, as they are called in England and the northern states of Europe; 3d, _lieutenant-generals_; 4th, _generals of division_, or major-generals, as they are called in England; 5th, _generals of brigade_, or brigadier-generals, as they are sometimes called;--colonels, majors, captains, lieutenants, ensigns, and cornets or cadets, are also either attached to the staff, or form a part of the _staff corps_.

The titles of "adjutant-general," and of "inspector-general," are given to staff officers selected for these special services, either in the general staff or in the several _corps d'armee_.

No special rank is attached to these offices themselves, and the grade of those who hold them is fixed by some special rule, or by their general rank in the army.
In the war of the Revolution, Washington held the rank of General, and in 1798 the rank of Lieutenant-general.