Defenitions
Engine is highest unit in pipeline. This provide initialisation of OpenGL and contains frames.
Frame is a 2D space in drawing window. For example, multiple frames can be used for visualise different data with different camera settings.
Frame contains scenes.
Scene is a container for objects. May be used for divide objects by a logical groups in frame.
Object is a drawable unit. That assembly from vertices, colors, normals, etc. For exaple this may be point, sphere, point cloud etc.