~ SMOW-TOWN ~
Kind of like this.....
But more like this...
...but actually this...
SMOW (aka "Standard Mean Ocean Water") - a standard measure of stable oxygen and hydrogen isotope values in present day seawater. It's used as a sort of baseline for what we know as the isotopic composition of water, against which we can compare other the isotopic oxygen and/or hydrogen containing materials to determine things about it like its age, place of origin, and history. Certain processes, biological (like eating corn!), hydrological (evaporation), and geological (the birth of sand beaches, y'all) included, preferentially sort some molecules based on their isotopic composition (because some isotopes make their molecules heavier than others).
This gives us a sense of the relative amount of 18O and D, and thus an idea of how much of an effect these process are having on the material.
In climate science, this is SUPER AWESOME because we can use it as a proxy for precipitation, temperature, wind patterns, and other COOL processes that indicate what big weather trends were like a bajillion (~50 million) years ago were like.