What is orthogonal signal? What is its physical meaning?

What is orthogonal signal? What is its physical meaning?

The so-called orthogonality refers to the wave pattern
If two waveforms integrate to zero over a period of time, they are orthogonal over that period
N orthogonal waveforms can form an n-dimensional signal space. The common m-PSK and M-QAM are two-dimensional band-pass signals; the basic signals are cos (2pifct) and sin (2pifct). Each point in the signal space represents an n-dimensional vector information, and the information is modulated to a specific point in the signal space