You have not concluded your merge (MERGE_HEAD exists)
Rant:
FFS Linus! Why did you have to make Git so complicated?
As others have pointed out. You need a bunch of arcane, inconsistent, constantly changing commands to do the most routine of tasks and the behaviour is counter-intuitive - why make vim the default editor?! Why make me learn all this stuff just to get things done?! *sigh*
No fucks given Linus:
The readme file of the source code elaborates further:
