This is the 118th most frequent German word.
einfach
Simple.
In this sentence, "einfach" is used as an adverb meaning "simply" to emphasize the extremity of balance of 'fantastic'.
Das ist einfach fantastisch.
That is simply fantastic.
Here, "einfach" is used in the comparative form, describing the solution as simpler, referring to its ease.
Ich brauche eine einfachere Lösung.
I need a simpler solution.
In this imperative sentence, "einfach" is used to suggest easiness or straightforwardness in completing an action.