Fingering
Indication of which finger plays a note.
What it means
Fingering indicates with which finger a note is pressed or struck. It is not a property of the music but a decision about its execution — the same passage can be fingered in different ways, and which solution is best depends on hand, instrument, tempo, and the desired shape of sound. Good fingerings therefore serve not only convenience: they help decide whether a line sounds connected or falls apart.
In the notation
On the piano and most keyboard instruments, numerals from 1 for the thumb to 5 for the little finger stand above or below the notehead. On string instruments 1 counts the index finger, 0 designates the open string; position indications in Roman numerals supplement the finger numerals. The guitar works with numerals for the fretting hand and letters for the plucking hand. With wind instruments, fingering indications are the exception and appear only for special fingerings. Fingerings supplied by the publisher are suggestions, not prescriptions; in Urtext editions they are identified, if they were added by the editor.
Musical use
A fingering solves two tasks at once. It makes the passage technically feasible — through thumb-under, change of position, distribution between both hands — and it secures the musical intention: a legato slur demands fingers that can hold the note until the next sounds, whereas phrasing off allows a change. In multi-voiced textures it decides which voice can be sustained tonally. It is therefore usually fixed only when tempo and phrasing are settled.
Performance practice
Fix your fingering early and write it in instead of fingering anew each time — the hand learns movement sequences, and changing paths prevent exactly that. Do not adopt printed indications unchecked: test them on your own hand and change what does not fit, but then change it bindingly. Place the points of change at rhythmically favourable spots, not in the middle of a fast run. And work backward from the goal: first it is settled how a difficult passage is to end, and afterward it follows how you get into it.