Okay, so let's imagine you are building a castle out of blocks. Before you start building, you need to have a plan. This plan is called a specification. It tells you what blocks you need, where to put them, and how to build the castle.
Just like building a castle, when people make things like software or machines, they need to have a specification too. The specification tells them exactly what they need to make and how to make it.
For example, think about making a cake. The recipe is the specification. It tells you what ingredients you need, the amounts, and the order to put them in. Without the recipe, you might not know what kind of cake to make, or what to add to it.
Specifications are important because they help make sure that things are built correctly and work the way they are supposed to. Without a specification, things might not work well or might not work at all!