diction
choice of words, especially with regard to correctness, clearness, or effectiveness. Any of the four generally accepted levels of diction-formal, informal, colloquial, or slang-may be correct in a particular context but incorrect in another or when mixed unintentionally. Most ideas have a number of alternate words that the writer can select to suit his purposes. "Children," "kids," "youngsters," "youths," and "brats," for example, all have different evocative values.

taken from here