What does 扩散 (kuòsàn) mean in English?

Card 1532HSK Level 41532/3571
CARD1532
PROGRESS43%
扩散
擴散
kuòsàn
diffuse(Verb)

Reveal: Click/Space/Enter/↑↓/w/s/j/kNavigate: ←→/h/l/a/d