Though it can be used two-handed (versatile weapon trait) in D&D 5e, as the longsword in real life, it is a bit too big in the picture. It looks a lot like the claymore swords as seen in the movie Braveheart.
Wikipedia says :
"The Scottish name 'claymore' (Scottish Gaelic: claidheamh mór, lit. 'large/great sword') can refer to either the longsword with a distinctive two-handed grip, or the basket-hilted sword developing from a rapier. The two handed claymore is an early Scottish version of a greatsword."
So the claymore is considered in between a longsword and a greatsword, which I am pretty sure is what is in this picture.
