The Theological Wordbook of the Old Testament (aka "TWOT") is edited by R. Laird Harris, Gleason L. Archer, Jr., and Bruce K. Waltke. TWOT is a 2-volume set, dealing with the Hebrew/Aramaic words in the Old Testament that have a theological significance. It gives a short definition to every Old Testament word, but goes theologically in-depth on the words that are considered to be necessary and noteworthy to clarity and contextual understanding of the Old Testament.

The TWOT uses its own numbering system that is tied to the more commonly available Strong's Exhaustive Concordance of the Bible, Hebrew identification numbers. To effectively use the TWOT, you simply look up the Strong's number in the Index section at the very back of each volume and take note of the corresponding TWOT number beside it. Use this number to locate the entry in either of the two volumes. Volume 1 contains TWOT numbers 1-1268, and Volume 2 contains TWOT numbers 1269-3067.

WHAT DOES THE NUMBER MEAN?
When using the lexicon on the free, online Blue Letter Bible for the Old Testament (https://www.blueletterbible.org/), one of the references cited is the TWOT. Here is the TWOT reference for the word bârâ' [Strong's H1254]:

TWOT - 278

The number refers to the entry number of the word. The word "bârâ'" is the 278th word in TWOT, Volume 1.

HOW DOES IT WORK?
According to the introduction inside the volumes, "The contributors were asked to study their words from the viewpoint of biblical usage, etymological background, comparison with cognate languages, translations in the ancient versions, synonyms, antonyms, and theological significance" (Vol 1, iv). While this was the focus of TWOT, not every major entry was able to include all of these features.