Electronic keyboards fall into well-established families or categories of instruments. Each has a relatively standard set of features and is meant to be used for specific musical needs and playing situations. Within each family, you encounter entry-level models that are more basic and then step-up models that add to the quality and number of sounds, number of features, size and quality of the keyboard feel, and so on:
Digital pianos: Acoustic piano wannabes or replacements.
Stage pianos: Digital pianos intended for the performing musician, with additional sounds and pro features.
Portable keyboards: Fun, lightweight, and full of features to help you sound better.
Arrangers: Keyboards with sophisticated backing features to produce the sound of a full band from your simple chord input.
Organs: Instruments dedicated to reproducing the sound, features, and feel of the legendary Hammond B3. They may include some additional sounds such as pipe organ, combo organs, and even other keyboard and synth sounds.
Synthesizers: Keyboards that allow you to make your own sounds and adjust the sounds provided. They can sound the most electronic and imaginative but now often include imitative and natural sounds as well.
Workstations: Basically, synthesizers with onboard recording systems to allow you to create complete works of original music. Very advanced and feature-rich.
Controllers: Keyboards that don't make sound themselves but are used to trigger sounds from your computer and other keyboards. These options use the MIDI standard to communicate with the sound-producing devices.