Definition: Any substance which can flow with relative ease, tends to assume the shape of its container, and obeys Bernoulli's principle; a liquid, gas or plasma.

Alright class, settle down, let’s take a peek, At the word “fluid,” something we need to speak! The dictionary gives us a helpful clue, “Any substance that flows, it’s true!” Now, think of water in a glass so bright, It takes the shape – a lovely sight! That's because it’s fluid , flowing free, Moving with ease for all to see. Let’s break it down, let’s make it clear, A fluid can be liquid, gas, or plasma here! Liquids like juice and oil, they pour, Taking the shape of what's in store. Gases like air – so light and fast, They spread out freely, built to last. Plasma , well, that’s a fiery state, Like stars and lightning, don’t hesitate! And Bernoulli’s principle? That's a bit more deep, It talks about speed and pressure, secrets they keep. A fluid moving fast will have less pressure, you see, it’s a fascinating decree! So, "fluid" means something can flow with grace, Taking the shape of its space! Do you understand? Any questions to share?