Definition of low-keyed:
(adj) :
Situated close to, or even below, the ground or another normal reference plane; not high or lofty.
(adj) :
Pertaining to (or, especially of a language: spoken in) in an area which is at a lesser elevation, closer to sea level (especially near the sea), than other regions.
(adj) :
(baseball, of a ball) Below the batter's knees.
(adj) :
Of less than normal height or upward extent or growth, or of greater than normal depth or recession; below the average or normal level from which elevation is measured.
(adj) :
Low-cut.
(adj) :
Not high in status, esteem, or rank, dignity, or quality. (Compare vulgar.)