2D cel animation and stop-motion animation both fall under the category of traditional animation, even if both may use digital methods of filming in the end. What matters is the method of producing the animation itself; cel animation generally involves hand-drawing, hand-inking, and hand-painting each frame on physical paper and cels, while stop-motion involves working with physical models and objects captured on camera one frame at a time.
Computer animation can be either 2D or 3D. 2D computer animation often involves a virtualization of the traditional 2D animation workspace, bringing pen and paper into the digital environment to recreate cartoon animation workflows and styles. 3D computer animation tends to involve a hybrid of workflows following traditional timelines adapted to working in a virtual 3D space. Either way, if you're animating on-screen you're working with computer animation.
In many cases it's hard to classify an animation as one or the other, as many animators take a hybrid path in which some parts of an animation are produced using traditional styles, then completed or enhanced using digital methods.

