Many database searches allow users to perform soundex searches. This allows users to look for names that "sound like" the name that was entered in the search box. This is great as long as you are aware of this and do not overlook reasonable variants of the last name in the process.
For this reason it is good to know the soundex codes for your last names and their variants. Not because you need them to search, but so you know what names you need to perform soundex searches for in order to not miss any results.
The last name Demoss occasionally gets written as Demop (because the "ss" is made like a "p" sometimes. A soundex search for Demoss will not bring up Demop because the two are not Soundex equivalent.
Demoss has a soundex code of D520
Demop has a soundex code of D510
Of course, Demos is a variant too, but since a double letter is omitted, there is no difference. Searching for "Demoss" with soundex turned on will not bring up any Demop refererences.
Rootsweb has a feature that will find the soundex code for your last names.