勃发 is a verb meaning 'to burst forth' or 'to surge'—describing a sudden, powerful, and often positive emergence of energy, emotion, or activity. The first character 勃 (bó) conveys vigor, intensity, or rapid growth (as in 勃勃生机 — 'vigorous vitality'), while 发 (fā) means 'to emit', 'to issue', or 'to start'. Together, they emphasize an abrupt, dynamic outpouring—not gradual development but an energetic upsurge.

This word is commonly used in formal or literary contexts to describe emotions (e.g., enthusiasm, anger, inspiration), natural phenomena (e.g., volcanic activity, spring blossoms), or social movements. It carries a slightly elevated register and is rarely used in casual speech. You’ll often see it after subjects like 热情 (enthusiasm), 怒火 (anger), or 生机 (vitality), and it frequently appears in written media, speeches, or descriptive prose—not in everyday dialogue.