A concordance is a list of words that appear in the Bible showing some of their context in addition to the references where they occur. This is probably one of the most valuable helps for studying the Bible. You can look up a specific word in your concordance and it will tell you which verses in the Bible contain that word. Some Bibles have a partial concordance printed right in them.
An exhaustive concordance (like Strong's Exhaustive Concordance) will have ALL the words in EVERY place of the Bible listed. Perhaps, the best concordances will be the search engine in a computer Bible program.