The study of fluids (liquids and gases) in motion, and the forces acting upon them. It's the science of flow, pressure, drag, and turbulence, essential for designing everything from submarines and aircraft wings to arterial stents and planetary weather models. In an alien context, it expands to "xenohydrodynamics," modeling how strange fluids—like liquid methane on Titan or supercritical carbon dioxide on Venus—behave under different gravities and temperatures. It answers questions about alien ocean currents, atmospheric circulation, and the design of vehicles meant to navigate non-water seas.
Example: Engineers using Hydrodynamics to design a silent submarine drone for exploring Europa's subsurface ocean must model how its shape interacts with salty water under immense pressure and near-freezing temperatures. An astronomer simulating the hurricane-force methane rivers flowing across Titan's surface is applying hydrodynamic principles to an alien fluid system.
While our lifespan is the number of years we will live, our healthspan is the number of healthy years we will have and our sexspan is is the number of years we will continue to be healthy enough to continue having an active sex life.
A lighthearted reaction upon receiving disappointing news of some sort. Usually something that isn't a particularly a big deal, esp. when it primarily affects someone else - sort of a mild schadenfreude. Sometimes doubled or tripled, and possibly said in a sing-songy voice for added comedic effect to imitate a muted trumpet, which is how the meme originated.