It's the community name for that Fromsoft weapon. If you just say Greatsword it's sometimes a bit difficult to know what you're referring to. People call that weapon Guts’ Greatsword (sometimes abbreviated as GUGS) since DS1, because it kinda looks like Guts' Sword from Berserk (manga).

Sword of Night and Flame is so busted and stylish, but also endlessly stat hungry. You can switch between optimizing for the Int and Faith skill by finally spending all your Larval Tears. Also only use the main weapon for trash mobs, for Boss fights it's really all in the Skill.

I'm unsure if it is ever truly outclassed in the Straight Sword Class. Spamming Square Off or Power-stanced attacks, is a whole other play style. But you can stack so many boost, especially in the end-game, on top of the two Skills for the ^Sword^ ^of^ ^Night^ ^and^ ^Flame^, that you one or two shot so much stuff.

The Guardian's Swordspear looks so cool. I almost switched to it in my first playthrough when it dropped, just because of how it looks.

In objective terms Guardian's Swordspear is quite good. It's the premier dex halberd and gets insane scaling with Keen infusion. I think Nightriders Glaive might me a bit better all around? Since it's has longer reach, but Nightrider's Glaive is definitely a strength weapon and doesn't look as cool as the Swordspear.

The wide swing of the Swordspear are a bit of an antithesis of a Fist weapon ;)