The terms Moslem and Muslim are often used synonymously being understood to have the same meaning. It might be true when considered by the English speakers as the two terms seem synonymous to them. However, for many others, the difference between the two is very significant that ultimately dictates their choice of word usage.
The difference between the two terms primarily emerges from their Arabic roots. The word Muslim refers to someone who gives oneself to God, and Moslem relates to anyone who is unjust and evil. This vast difference between the two words, when seen from the Arabic point of view, is the significant reason why many people have shifted to the use of the term Muslim instead of Moslem.