This is the 4976th most frequent Russian word.
крепость
Fortress.
The word "крепость" here refers to a fortified structure, a castle or stronghold.
Крепость на вершине горы была построена много веков назад.
The fortress atop the mountain was built many centuries ago.
Here, "крепость" metaphorically represents strength or resilience of character.
Его крепость духа помогла ему преодолеть все трудности.
His strength of spirit helped him overcome all difficulties.
In this context, "крепость" refers to the strength or potency of wine.