This is the 562nd most frequent Finnish word.
terveyden
"Terveyden" means "of health" in English.
The word 'terveyden' is the genitive case form of 'terveys' ('health') and is used here to indicate possession or association, as maintaining pertains to health.
Terveyden ylläpitäminen vaatii säännöllistä liikuntaa.
Maintaining health requires regular exercise.
Here, 'terveyden' again denotes possession or association, showing that the advocacy is on behalf of the patients' health.
Lääkäri puhuu aina potilaidensa terveyden puolesta.
The doctor always advocates for the health of their patients.
In this sentence, 'terveyden' specifies the object of concern, showing care or focus on health.