People who use the term "delta" to mean either "change" or "differential" in spoken language.
If you are and engineer, or if you work with them, you have probably experienced this. First of all, the mark of a mature, intelligent person is the ability to communicate at least moderately technical information to the lay person in common language. Second, unless your audience is made up of engineers, they are not going to understand your meaning. This is not because it is complex, but because you are simple. Finally, unless they are as pretentious as you are, they think you sound stupid.