Terraced dynamics, a unique characteristic of Baroque music, has to do with a quick alteration in tempo or volume that does not involves a progressive crescendos and decrescendos. The harpsichord, the basic keyboard tool of the era, could majorly perform forte (loud) or piano (soft) only, and couldn't perform crescendo or decrescendo in between, and thus results in a quick shift in dynamics. It is a specific character of music that represents it's success.
In some cases, they were highlighted in the score, but a large sort of area, it was agreed upon mostly by the performers or were directed by conventions which was fully expressed to all musicians.
