Which expression marking indicates smooth and flowing music?

The expression marking that indicates smooth and flowing music is "legato." When a passage is marked legato, it instructs musicians to play in a connected manner, where each note seamlessly transitions into the next without any perceptible breaks in between. This creates a gentle, flowing quality in the music, allowing the melodic lines to sound cohesive and fluid.

In contrast, staccato, which is another marking, signifies short and detached notes, creating a distinct separation between them rather than the smoothness associated with legato. Marcato indicates a more forceful or accented style of playing, encouraging an emphasized articulation of notes, which also detracts from a smooth quality. Tenuto, while it suggests that a note should be held for its full value, does not necessarily imply the same level of connectedness as legato, and can still allow for some separation between the notes. Therefore, legato is specifically designated to convey that smooth and flowing characteristic in music.