The particle "を (wo)" is used in the Japanese language to indicate the direct object of a verb. It marks the noun that receives the action of the verb, helping to clarify what is being acted upon. For example, in the sentence "りんごを食べる" (I eat an apple), "りんご" (apple) is the direct object, and "を" shows that it is the item being eaten. In addition to its grammatical function, "を" can also appear in various contexts, such as in phrases indicating movement through a place. For instance, in "公園を散歩する" (I walk in the park), "公園" (park) is marked by "を" to show the location of the action.