a multi-colored coat or similar garment or covering; something that makes others envious
—My favorite time of year is spring, when the flowers bloom and my mother’s garden is clothed in a coat of many colors.

God changed Jacob’s name to Israel and blessed him with 12 sons. Of these sons, Joseph was Israel’s favorite, and he showed this by giving Joseph a special gift:

Now Israel loved Joseph more than all his sons because he was a son born to him late in life, and he made a special tunic for him [a coat of many colours—KJV]. When Joseph’s brothers saw that their father loved him more than any of them, they hated Joseph and were not able to speak to him kindly. (Genesis 37:3,4)

Over time, the brothers’ anger toward Joseph increased, until one day they sold him to some merchants who took him as a slave to Egypt. When the brothers went back to their father, they told him that Joseph had been killed by a wild animal, convincing Israel of this by showing him Joseph’s coat, which they had dipped in the blood of a goat.