What is the difference between a word and a wording?

Word (字) is a single word
Wording (用語) is the composition of words in a phrase, sentence for a good style of expression.
e.g. word : work wording : work hard, difficult work, work in a good style . You will note that work, hard, difficult, good, style are also a word while "in a good style is a phrase" etc. etc. for sentence, paragraph and even a passage.
You can then get a much clear expression from the writer or speaker if you use good and proper wordings in expressing yourself. In above, if you use difficult work, it is not an easy work for you then.

word=詞,單字
wording=措辭;用語