This is the 5057th most frequent Dutch word.
hoog
"Hoog" means "high" in English.
In this sentence, 'hoog' is an adjective describing the height of the mountain.
De berg is hoog.
The mountain is high.
Here, 'hoog' describes the high pitch of the singing, used as an adverb modifying how he sings.
Hij zingt erg hoog.
He sings very high.
In this context, 'hoog' is used metaphorically to express the idea of elevated standards or expectations.