I'm currently reading a legal document which refers to 'wet' shipping/work/practices. In the first instance, the meaning of 'wet' is explained. Can the quote marks be omitted thereafter?
Punctuation is a matter of style, and as such the writer is guided by the governing manual of style. I use the Chicago Manual of Style, which recommends that technical terms appear in italic when they're defined and in roman thereafter. When the term is a specialized use of a common word, the recommendation is place the the word in quotes instead. Presumably, the quotes are unnecessary thereafter. But bear in mind that you're reading a legal document, and lawyers are fond of redundancy to make things clear. If there's the slightest chance that wet work might be interpreted differently from "wet" work, a lawyer will prefer the latter to the former.