This is the 988th most frequent Ukrainian word.
їхнє
"Their" (possessive pronoun).
In this sentence, 'їхнє' acts as a possessive pronoun denoting possession of the noun 'хобі' (hobby) by a group.
Їхнє улюблене хобі - подорожувати.
Their favorite hobby is traveling.
Here, 'їхнє' indicates possession of the noun 'рішення' (decision) by the owners.
Ми спитали про їхнє рішення щодо цієї справи.
We asked about their decision regarding this matter.
In this case, 'їхнє' shows possession of 'життя' (life) by a group.