Here's why:
* It modifies a verb, adjective, or another adverb: It tells us *how* something is moving or directed. For example:
* "The rocket moved upward." (modifies the verb "moved")
* "The upward trend in prices is concerning." (modifies the adjective "upward")
* "The bird flew upward quickly." (modifies the adverb "quickly")
Let me know if you'd like more examples!