I am a bit confused about this because my teacher and english Wikipedia say it's the wavelenght the Photosystem is most reactive to; my textbook and the german Wikipedia say that it is the maximum wavelenght the Photosystem can absorb :-/
I'd first like to briefly mention what the P700 and P680 refers to. These are the reactions centers of the photosystems. The Photosystems are where the light is absrobed and converted to the form of electrons. The light is absorbed by the chlorophyll molecules and the energy is transferred to the reaction center which transfers that energy into an electron from a water molecule. Tha elecron is transport tmake ATP and NADPH, which is important for carbon fixation.
The numbers specify the wavelength of light that the reaction center are most reactive to, and therefore, the wavelength where they absorb the most light. That's what's meant by the maximum absorption. So everybody is right, your teacher, the textbook and Wikipedia. They just say it differently.