The word through functions primarily as a preposition. It is used to indicate movement from one side to another, or to describe a passage across a space or condition.
For example, in the sentence, “The cat ran through the garden,” the word through shows the cat’s movement that crosses the garden.
Additionally, through can also serve as an adverb, particularly in phrases like “come through,” meaning to successfully complete a task or fulfill a promise. In this way, it hints at the idea of passing from one state to another.
In summary, through is mainly a preposition but can also be used as an adverb in certain contexts.