means Letting light pass through so you can see what's on the other side — or, figuratively, being open and easy to see through, with nothing hidden.

from From Latin 'transparere,' literally 'to show through' — 'trans-' (across, through) plus 'parere' (to appear, come into view). It entered English through Medieval Latin 'transparens,' and for centuries was a strictly physical word about glass and water; the metaphorical sense of honest, undisguised people and institutions is a much later stretch of the same idea — you can see right through them.