Quarter note
A quarter of a whole note; in most time signatures the beat.
What it means
The quarter note lasts a quarter of a whole note, that is, half of a half note and twice an eighth note. In most time signatures — 2/4, 3/4, 4/4 — it is the beat and thus the pulse by which counting and conducting are done.
Like all note values, it designates a ratio, not a fixed duration. Metronome markings most often refer to the quarter, which is why the sign ♩ is so widespread in tempo markings. Dotted, the quarter yields three eighths; in compound time signatures such as 6/8, it is exactly this dotted quarter that is the beat, while the plain quarter there makes up two thirds of a beat.
In the notation
The quarter note has a filled-in notehead and a stem, but no flag. This distinguishes it from the half note, whose head is open, and from the eighth note, which carries a flag. The stem goes up to the right up to the middle line, above it down to the left; in multi-voice systems it is oriented by the voice.
The corresponding quarter rest has its own, jagged sign, which stands in the middle of the staff.
Musical use
The quarter is the most common note value of all. It carries walking bass lines, melodies with calm movement, and the beat in almost all simple time signatures. In chorales and songs the text mostly lies syllable by syllable on quarters, which makes singing along easier. Because it is the reference value for tempo markings, it also serves as a common unit of understanding within the ensemble.
In many time signatures it forms the beat. In English it is called the quarter note.
Performance practice
Use the quarter as a reference pulse when you work out a passage, and derive smaller and larger values from it. Take care that quarters in walking basses are really equal in length — they easily become unequal as soon as the upper voice has smaller values. Check, with a metronome marking, whether it actually refers to the quarter. And distinguish carefully, when reading, between a filled and an open notehead.