Properly speaking, a crucifix is a cross to which there is attached, in relief, an image of the body of Christ. However, if the figure is painted, impressed, or otherwise represented, it is classed as a crucifix.
A crucifix should be placed over an altar where Mass is celebrated; it is recommended that there be a crucifix in each home; and a crucifix is attached to the pendent portion of all rosaries.
The skull seen upon some crucifixes is not essential to the crucifix; it is simply a symbol of Calvary (the place of the skull). More proper is the tablet or banner, called the “title,” attached near the top of the upright beam, bearing the letters I.N.R.I., the initials of the Latin words for “Jesus of Nazareth, King of the Jews.”
Special indulgences are attached to the crucifix and to certain prayers recited before it. In the liturgy a crucifix upon a standard called a “processional cross,” is carried into the sacred area at the time of the entrance procession. (7:39)