Wat is a periodic wave function?

Explanation

A wave fnction `y(x,t)` which satisfies that periodicity conditions of position and time is called a periodic wave function, i.e.,
(i) `y(x+mlambda,t)=y(x,t)`
(ii) `y(x,t+nT)=y(x,t)`
where `lambda=` wavelength of wave, `T=` period of the wave, n and m are integers.