This is the 12873rd most frequent German word.
zach
"Zach" is not standard German; it may refer to a surname or regional slang, possibly meaning "tough" or "slow" depending on context.
In this sentence, 'zach' is used as an adjective describing the cake's texture as hard or tough.
Der Kuchen war zach; ich konnte ihn kaum schneiden.
The cake was tough; I could barely cut it.
Here, 'zach' is used metaphorically to describe a manner of speaking as rough or unrefined.
Sie spricht immer zach, wenn sie aufgeregt ist.
She always speaks in a gruff manner when she is excited.
In this case, 'zach' describes the snapping or brittle texture of the frost-covered grass.