This is the 40th most frequent Russian word.
очень
Very.
The word 'очень' is used here as an adverb to intensify the adjective 'cold' in the sentence.
Сегодня очень холодно.
Today it is very cold.
In this sentence, 'очень' is utilized as an adverb to enhance the emotional expression conveyed by the word 'glad'.
Я был очень рад тебя видеть.
I was very glad to see you.
Here, 'очень' serves as an adverb modifying the adjective 'interesting' to emphasize the quality of the book.