A splash is a tiny amount of a liquid. You might, for example, prefer your coffee with just a splash of cream.
A splash can be wet, like a splash of lemonade in your tea, or it can be bright, like a splash of yellow across the oil painting you're working on. You can also use splash as a verb, as when you splash your sunbathing brother with swimming pool water. Splash first appeared in the early 1800's as a variation on the word plash, which had the same meanings and is most likely imitative — in other words, it sounds like its meaning.