Eighth note
An eighth note (in British terms a quaver) is a quarter note with a flag on its stem. It lasts half a beat, so two eighth notes fit in one beat.
An eighth note splits the beat in two: two sounds in the time of one quarter note. We count them with an “and” between the beats: one, and, two, and, three, and, four, and. The beats stay on the numbers, and the second eighth comes on the “and”. In syllables a pair of eighths is ti-ti, a quarter note ta.
When eighth notes stand side by side, their flags are replaced by a thick line joining the stems: the beam. It sounds exactly the same but is easier to read — you see at once which notes make up one beat. A single eighth note with no partner keeps its flag.
The eighth note has its own rest too: the eighth rest, half a beat of silence. In 6/8 time the eighth note is the counting unit and is beamed in threes.
What it sounds like
Eighth notes sound twice as busy as quarter notes: “ti-ti” instead of “ta”. The beat does not get faster — more notes simply fit inside it.
Where it is taught: the studio’s interactive textbook, chapter 12, “Eighth notes and the dotted quarter” and chapter 14, “6/8 and the waltz pulse”.