Okay kiddo, so an aliphatic compound is kind of like a Lego toy. You know how you can take the Lego blocks and snap them together to make different shapes and structures? Well, aliphatic compounds are made up of smaller building blocks called "alkyl groups" that can be snapped together in different combinations to make lots of different types of molecules.
These molecules are called "aliphatic" because they don't have any rings in their structure - they are just long chains of carbon and hydrogen atoms. Think of it like a really long string of beads, where each "bead" is a carbon atom and the "string" is a chain of linked atoms.
Aliphatic compounds are found in lots of different places - in gasoline, for example, or in the waxes that bees make for their hives. Some aliphatic compounds are even used in medicine to make drugs that can help people feel better when they're sick.
So, if you ever hear somebody talking about "alkanes", "alkenes", or "alkynes", just remember that they're all different types of aliphatic compounds - just like how different types of Lego blocks can be combined to make different toys!