What is the meaning and translation of my niece's name?
Probably it is because it was a leap year (闰年). 闰 and 润 have same pronunciation, which is similar to English word 'ruin' (even the tone is the same) but shorter.
闰 means intercalation and 润 means moist, smooth literally and nurturing, nourishing/nourished prosperity and affluence figuratively. 润 is often a good word and commonly used in people and organization names.