Vachement is an adverb derived from the word vache, which means “cow”. Its meaning, however, has absolutely nothing to do with cows. It basically means “very” and it is extremely common in colloquial French.
Il est vachement grand ton appartement !
Your flat is really big!
Il est vachement bien, ce bouquin !
This book is really great!
Vachement de means “a lot of”.
Je bosse chez moi, ça me fait gagner vachement de temps.
I work at home, it makes me spare a lot of time.
Listen to the examples: