Hatzlachah means success and is one of those words that have made it into everyday speech among English-speaking Yeshivish Jews.Thus on parting ways, one friend might say to the other, hatzlachah rabbah, much success!
The biblical Joseph has a strong association with hatzlachah.We are told that in the house of Potiphar, The Lord was with Joseph and he was a successful (matzliach) man (Genesis 39:2). Potiphar invested him with increasing responsibilities because the Egyptian saw that the Lord was with him and the Lord lent success to everything he undertook. Even in jail, Josephs hatzlachah was obvious. The source of his success is the fact that God is with him. Potiphar and the jailer both realise that Joseph is not simply a talented guy but a recipient of Gods grace. Hatzlachah denotes success due to divine providence.
The word derives from the root tzalach, whichmeans to rest on, as in the spirit of prophecy. After Samuel anointed Saul, the spirit of God gripped (vatitzlach) him (I Samuel 10:10). An additional meaning is to cross or rush forward; and Ziba rushed (vtzalchu) down to the Jordan (II Samuel 19:18). Prophecy and moving forward are both signs of success. Wishing someone hatzlachah is a powerful blessing, and in comparison the banal English equivalent Good Luck! seems a lame offer of encouragement.