The Baroque musical period
Baroque music is that in which the harmony is confused, and loaded with modulations and dissonances. The singing is harsh and unnatural, the intonation difficult, and the movement limited. It appears that term comes from the word "baroco" used by logicians.
The concept of writing music in a particular key came to fruition in the Baroque period, this is also known as common-practice tonality. Professional musicians in this era were adept in the art of improvisation, both of melodic lines and of accompaniment parts. Accompaniments comprised of chordal instruments like the harpsichord and lute, and bass instruments like the viola, cello and double bass - these players made up what was known as the basso continuo group. The basso continuo played improvised parts by reading music known as figured bass. This setup has similarities to modern jazz and pop music, whereby a rhythm section creates an accompaniment from chord symbols.
Composers increasingly used chord progressions to create music in the Baroque period, they also introduced more dissonant sounds by including the tritone interval in dominant 7th and diminished chord types. The concept of harmonic resolution was firmly established through the concept of the cadence whereby the end of a musical phrase used cadential chords to bring a harmonic sequence to finality, thus grounding the music in a particular key.