This is the 4923rd most frequent German word.
alb
"Alb" in German means "nightmare."
In this sentence, 'Alb' refers to a 'nightmare,' which is its old-fashioned or poetic usage in German.
Ich träumte von einem düsteren Alb.
I dreamed of a dark nightmare.
Here, 'Alb' refers to a geographical feature or region, such as Swabian Alb in Germany.
Die Alb erstreckte sich über weite Hügel und Täler.
The Alb stretched over wide hills and valleys.
This use of 'Alb' refers to a mythical or folklore creature, an elf or sprite.