Hi trance999, keyboard is a generic term for all instruments with black and white keys - including acoustic and electronic. Therefore, piano is a keyboard. So is the organ, harpsichord, synthesizers etc.
What people usually term "keyboard" is really the electronic keyboard. If you are thinking of picking up the instrument and cannot decide between acoustic and electronic, you really need to ask yourself what music you'll be playing - like what utano said.
Besides the touch of the keys (ie weight etc), there are many other differences between the 2, electronic having more functions.
Electronic keyboards come in different number of keys - 49, 61, 78, 88 - some less. Besides Fatar keyboards, all other brands weighted keys (ie feel heavy) comes only as 88 keys. The other with less keys are lighter in touch. But no matter how many keys, the keyboard will ALWAYS centre around middle C (ie C3 or C4 depending on which standard you are using). However, keyboards with less keys are usually transposable - ie you can switch the octaves such that the middle C changes position.