Middle C - The note C in the middle of the Grand staff, and near the middle of the piano.
Poco - Little. Used with other terms, e.g. poco accel., also, poco a poco, little by little.
Romanticism - The period c. 1825-1900.
Seventh chord - When a seventh (above the root) is added to a triad (root, third, fifth), the result is a seventh chord, e.g. the dominant triad in the key of C major, g-b-d, with the added seventh becomes g-b-d-f and is labelled V7.
Tone - A note; the basis of music.