Q. Why do some people write “G-d” instead of “God”?
A. Actually no phrase is good enough to express the Creator’s full greatness. The Torah (Ex. 15:11) calls Him nora tehillot – “awesome in praises”, which Rashi explains as meaning “that people are afraid to praise You, lest it be insufficient”. So whatever way we address God is only an attempt.
From the Torah (Deut. 12:3-4) we learn that it is forbidden to erase the name of God. Hence, anything containing the Divine name must be treated with respect and not erased, destroyed or discarded. Worn-out religious texts and scrolls are therefore saved and eventually given reverent burial.
In strict law the prohibition is limited to the actual names of God in Hebrew (Shach on Shulchan Aruch, Yoreh De’ah 179:11, 276) but not to renderings in other languages such as Gott in German or God in English. However, many authorities extend the law to cover Divine names in any language, which is how the practice of writing “G-d” began; if something bearing this defective spelling is discarded it is not viewed as seriously as if the full spelling is used.
The practice I employ is to write simply “G” in notes, etc., but in books, articles and in OzTorah I spell the word in full – “God”, “Lord”, etc.
The Rema prohibits writing words such as Shalom, since God is the Lord of Peace (YD 276, end), but if the word is written in a secular sense and not as a reference to God, it may be written normally (Pit’chei T’shuvah). Rav Moshe Feinstein (Ig’rot Moshe, YD 2:138) warns against writing Bet-Hey at the top of a page since Hey is a hint of a Divine Name; it is better to use Bet-Samech-Dalet, which stands for “With the help of Heaven”.