Expression
Fine nuancing of tempo, dynamics, and tone color in performance that goes beyond the written notation.
What it means
Expression is the fine nuancing of tempo, dynamics, tone color, and phrasing in performance that goes beyond what notation can fix in detail. Two performers playing the same notes can achieve entirely different effects through different expression.
Expression is therefore not an extra ornament but what turns a performance into an artistic act in its own right. It grows out of an interpreter's reading of tension and release, harmonic goals, and rhythmic weight that the written score only hints at.
Musical use
Since the eighteenth century, composers have increasingly tried to steer expression through performance markings such as espressivo, dolce, or con affetto, and through detailed dynamic and articulation markings, without ever fixing it completely. In the eighteenth-century empfindsamer Stil and later in Romanticism, expression moved to the foreground as an aesthetic ideal: music was meant to convey feeling directly, not merely display skillful construction.
Expression should be distinguished from mere technical correctness; a flawlessly but expressionlessly played piece is generally felt to be unsatisfying. It also differs from rubato and dynamics, which serve as concrete musical means toward expression without exhausting it: expression names the overarching goal, rubato and dynamics the tools used to reach it.
Performance practice
Before practicing a piece, look for its inner arcs of tension: where is a phrase heading, which note carries the weight? Use deliberate shifts of tempo and volume, but sparingly enough that they remain audible as artistic choices rather than dissolving into arbitrariness.