Keriah
The torn garment, usually a shirt, jacket or vest that "covers the heart," is worn throughout the shiva period (a practice known as "keriah"; alternative spellings "keriyah", "kria"), except on Shabbat. Conservative and Reform Jews will usually wear a torn piece of black ribbon instead of a torn garment. The torn garment symbolizes/expresses the grief of the mourner.
Read more about this topic: Shiva (Judaism)