When I cover dynamics and loudness in music theory class, I only spend a small part of the time talking about forte/piano, crescendo/diminuendo and so on. Once you have the Italian translations, those terms are self-explanatory. They are also frustratingly subjective, and they refer only to unamplified acoustic music. To understand dynamics in the present day, you need to understand decibels, perceptual loudness, and what “dynamics” mean in the era of recorded, amplified and electronic music.
First of all, let’s talk about the classical terms a bit. When you see that classical music uses “piano” to mean “quiet,” you might naturally wonder what the relationship is to the instrument. The piano’s inventor, Bartolomeo Cristofori, originally called it “un cimbalo di cipresso di piano e forte,” meaning “a keyboard of cypress with soft and loud”. This got variously abbreviated as fortepiano, pianoforte, and finally, its current name. This was all in contrast to the piano’s predecessor, the harpsichord, which can only play at one volume.