半 means half. 斤 is a unit of measurement, in English it’s known as a catty. 八 means eight and 兩 is another unit of measurement, in English it’s known as a tael.
You could translate this quite literally into “Half a catty, eight taels”. Now the interesting part. Half a catty is equal to eight taels. This phrase is often used as a reply to someone, to indicate that two situations or things sound different but are equal.
This phrase has been used since the Song dynasty. This phrase is identical to the English phrase “six of one, half a dozen of the other”. Were the two phrases independently coined? I have no idea.