A two-barred cross is like a Latin cross with an extra bar added. The lengths and placement of the bars (or "arms") vary, and most of the variations are interchangeably called either of cross of Lorraine, the patriarchal cross or the archiepiscopal cross.
The two bars
The two bars can be placed tight together (condensed) or far apart. They can be symmetrically spaced either around the middle, or above or below the middle. One asymmetrical variation has one bar near the top and the other just below the middle. Finally the bars can be of equal length, or with one shorter than the other.
The ends of the arms can be decorated according to different styles. A style with round or rounded ends is called treflée or botonée (from French bouton) in heraldic use. The same style is called budded, apostles' or cathedral cross in religious use. A straight and pointy style called pattée also includes maltese cross variations, and finally a pointed style called aiguisé.
The crosses appear in heraldic use in the second century A.D. A balanced cross is used in the Coat of arms of Hungary as well as in several small shields within shields of Vytis. An outlined balanced cross (equal length outlined bars on equal distances) is used on coat of arms shields and order medals 
In Slovakia both the flag, their coat or arms and several municipal symbols include a double cross, where graded bars are more common than equally long bars, and balanced distances along the vertical line are more common.
In typography the double cross is called double dagger, double obelisk and diesis.
In medicine and botany
The International Union Against TB and Lung Diseases is since 1902 using a red cross variation in its logotype. The two equally long bars are on the upper half of the cross and all six ends are aiguisé.