油を売(る means wasting time when you should be working. It often describes dawdling, chatting, or doing something unrelated to the job.
In English, “loafing around” has a similar meaning.
Literal Meaning
The literal translation is “selling oil”. The expression is believed to derive from the Edo period (1603–1867), where oil merchants would sometimes engage in lengthy small talk with women while selling oil to them.