Sentence:  After the third or fourth spraying session (about 10 coats of lacquer), and after the finish has cured for at least 48 hours since the last spraying session, you can begin to <WSD>wet sand</WSD> the finish. 
Meaning of the word marked with <WSD> tags:  To sand using extremely fine-grained sandpaper, using a lubricant such as water or oil to prevent the sandpaper from clogging.