This is the 71st most frequent Croatian word.
oni
"They" (third person plural pronoun).
Here, 'oni' is used as a pronoun referring to a group of males or a mixed group in the nominative case serving as the subject of the verb 'idu' (go).
Oni idu u školu svaki dan.
They go to school every day.
In this sentence, 'one' is a form of 'oni' used as a demonstrative pronoun referring to 'ljude' (people), in the accusative case since it is the object of the verb 'vidjeti' (to see).
Jesi li vidio one ljude tamo?
Did you see those people over there?
Here, 'oni' is used again as a pronoun in the nominative case, referring to a group of entities (in this case 'psi', dogs) introduced in the previous sentence.