bu̍t-lí-ha̍k, chi̍t-ê pho-tōng (Eng-gí: wave), sī kóng chi̍t hāng kiáu-jiáu, i thang keng-kòe bu̍t-chit ia̍h khong-kan, tī m̄-bián ia̍h chió-liōng chit-liōng ūn-sàng ê chêng-hêng thoân-sàng lêng-liōng. Pho-tōng sī bu̍t-lí kài-chit ia̍h tiûⁿ (field) ùi siong-tùi kò͘-tēng ūi-tì ê lō͘-nì-hi̍t (oscillation) ia̍h sih-chùn (vibration).