3D animation is the process of creating three-dimensional models frame by frame . This is done by creating a model or character, rigging it with bones and joints, and then animating it to create the desired movement.
CGI is the process of creating images or scenes using computer graphics. This can be done by either generating the images from scratch or by manipulating existing images and can be used to create anything from simple 2D images to complex 3D environments.
The key difference between CGI and 3D animation is that CGI uses three-dimensional objects to create the illusion of movement while 3D animation involves the construction of three-dimensional models frame by frame. 3D animation and CGI both have their pros and cons, so it really depends on what you're looking for in a visual effects solution. If you want to create static images, then CGI is a good choice. If you want to create the illusion of movement, then 3D animation is a better choice.