St. Hillary has a great explanation of what is meant by "Fear of the Lord." This comes from the Liturgy of the Hours' Office of Readings on Thursday morning.
"'Fear' is not to be taken in the sense that common usage gives it. Fear in this ordinary sense is the trepidation our weak humanity feels when it is afraid of suffering something it does not want to happen. We are afraid, or are made afraid, because of a guilty conscience, the rights of someone more powerful, an attack from one who is stronger, sickness, encountering a wild beast, suffering evil in any form. This kind of fear is not taught: it happens because we are weak. We do not have to learn what we should fear: objects of fear bring their own terror with them.
But of the fear of the Lord this is what is written: Come, my children, I shall teach you the fear of the Lord. The fear of the Lord has then to be learned because it can be taught. It does not lie in terror, but in something that can be taught. It does not arise from the fearfulness of our nature; it has to be acquired by obedience to the commandments, by holiness of life and by knowledge of the truth.
For us, the fear of God consists wholly in love, and perfect love of God brings our fear of him to its perfection. Our love for God is entrusted with its own responsibility: to observe his counsels, to obey his laws, to trust his promises. Let us hear what Scripture says: And now, Israel, what does the Lord your God ask of you except to fear the Lord your God and walk in all his ways and love him and keep his commandments with your whole heart and your whole soul, so that it may be well for you."