is the znear and zfar that I specify in
ortho (T const &left, T const &right, T const &bottom, T const &top, T const &zNear, T const &zFar)
Is it in camera space or in world coordinate system?
The coordinate system is whatever is used by the coordinates you’re transforming with the matrix.
The transformation created by glm::ortho() will transform Z=-zNear to Z=-1 and Z=-zFar to Z=1.