A lot depends on what you want. Do you want a keyboard that sounds and feels like a Piano – then you’re looking for a keyboard or Digital Piano with WEIGHTED keys. Listen carefully to the piano sound – don’t be bamboozled by all the other buttons. If you want something portable then you are looking for a keyboard. Personally I would still look for one with weighted keys – I hate the feel of light plastic keys.
Get a keyboard with at least 61 keys – anything less and you will be craving for more keys after a few days. Also make sure get a sustain pedal, a keyboard is absolutely a dead thing without one. Without a sustain pedal as soon as you lift your finger off a key the sound stops dead – with a piano at least the strings vibrate for a second or two – the difference is quite noticeable.