Hello Roy,
The date is the date carved, or engraved, on to the tang of the sword by the swordsmith. In the case of this sword, the tang has the Japanese date of "Showa 18, June". Showa is the old era name, so "Showa 18" means the 18th year of the era of Showa, which corresponds to the western calendar year of 1943, as I mentioned in my post above.
So this sword was made in June of 1943.
On the opposite side is the name of the swordsmith; Yoshikuni (or 義国 in Japanese characters). I thought there would be more than just two characters for the swordsmith's name, but I guess there are just the two.