Caesura
Two slashes (“railway tracks”), a short general pause.
What it means
The caesura is a break: at the marked spot the musical flow stops for everyone involved, a brief silence arises, and then playing continues. Unlike a notated rest, it has no measured value — its duration is determined by the conductor or, in chamber-music ensemble playing, by the leading voice. Meanwhile the beat does not continue; time stands still, as it were, until the cue to continue is given.
In the notation
The sign consists of two parallel slashes placed above the top staff line or through it; in colloquial usage they are called “railway tracks” because of their appearance. In scores the sign is usually placed above the top staff and is additionally repeated in the individual parts. Related but to be distinguished are three other signs: the breath mark, a single comma that only articulates within one part and takes its time from the preceding value; the general pause, which stands as a written-out rest in the bar and is therefore counted; and the fermata, which prolongs a sound or a rest instead of interrupting the flow.
Musical use
The caesura is used at places where a section comes decisively to an end and something else begins — before a change of theme, before the entry of a new key, before the closing section of a movement. Its effect rests on expectation: the ear counts on a continuation and at first gets nothing. In wind literature and choral music it also serves practically as a shared moment for breathing. In older sources the sign is often missing, although the music suggests such a break; the decision then lies with the performers.
Performance practice
Fix the length of the silence in the ensemble beforehand instead of feeling it out anew each time — a caesura that not everyone takes equally long sounds like a mistake. Take care to end the note before the break cleanly and not to let it fade away; the break begins with a deliberate ending, not with petering out. Take the entry afterwards clearly, ideally with a shared breath. And count in anew after the caesura: whoever has kept counting inwardly comes in too early.