phonetics
/ fuh-NET-iks /
Phonetics is the study of the actual sounds of speech — the real, physical noises your mouth makes. It looks at three things: how a sound is built (lips, tongue, breath, and voice box working together), how it travels through the air as a wave, and how the ear catches it. Say "pin" and then "bin" and rest a finger on your throat: for the "b" in "bin" you can usually feel more vibration than for the "p" in "pin". That vibration, the buzzing of your vocal folds, is exactly the kind of physical detail phonetics measures — and it is a separate feature from the little puff of air in the example below.
This matters because it gives us a way to describe any sound in any language with precision, no matter how it happens to be spelled. The same "sh" sound shows up in English, French, and German; phonetics gives it one agreed symbol and one bodily description, so a speaker of any language can reproduce it. It is the toolkit behind language teaching, speech therapy, voice recognition, and the careful study of accents.
Here is the common mix-up: phonetics is not the same as phonology. Phonetics studies the raw sounds themselves — the physics and the plumbing. Phonology studies how a particular language organizes those sounds into a meaningful system: which differences change a word's meaning, and which the ear simply ignores. Phonetics asks what a sound is; phonology asks what a sound does inside a language.
The "p" in "spin" and the "p" in "pin" are physically different sounds — only "pin" has a little puff of air — yet English treats them as the same letter.
Phonetics hears two sounds; English spelling, and its phonology, hears one.
The word comes from the Greek phōnē, "sound" or "voice." Phoneticians often split the field into three parts that follow a sound on its journey: articulatory (how the mouth makes it), acoustic (how it travels as a wave), and auditory (how the ear and brain receive it).