呼吁 (hū yù) is a verb meaning 'to appeal' or 'to call on (the public, authorities, or a group) to take action, often for a cause considered urgent or morally important.' The first character 呼 (hū) means 'to shout' or 'to call out,' and the second 吁 (yù) also carries the sense of 'to appeal' or 'to implore' — together they form a compound emphasizing vocal, public, and earnest entreaty. Unlike casual suggestions or requests, 呼吁 implies collective concern and often appears in formal or activist contexts, such as environmental protection, animal welfare, or social justice.

This word is commonly used with objects like 'the government,' 'the public,' or 'international organizations,' and frequently follows subjects like NGOs, scientists, or concerned citizens. It’s rarely used in everyday personal conversation but appears regularly in news reports, petitions, speeches, and advocacy campaigns. While both characters individually can mean 'to call,' only the combination 呼吁 functions as this specific formal verb — using either character alone in this sense would be incorrect or unnatural.