Prior to the invention of the piano there was an instrument called a harpsichord which was played by playing a keyboard but the result was plucking of the strings similar to a guitar. And prior to the harpsichord there was an instrument call the psaltry which was played by actually plucking the strings. Later the psaltry had a keyboard, and that led to the harpsichord.When the piano was invented somewhere around 1700, it was novel in that instead of the strings being plucked they were struck by a hammer which was inside the piano.As a result music could be played both soft and loud which was not true with the harpsichord or the sultry. So it was named the "pianoforte" which in Italian means the "soft loud instrument." It was refered to this way for many years until finally the "forte" part of the name was left off and was just refered to as the "piano." Kind of strange in a way, since in Italian the word piano means soft. So to be literal, you are playing the "soft." when you play the piano, even though you play it using a variety of dynamics.
