A category is a set or class of things having some property or attribute in common and differentiated from others by kind, type, or quality. There are many different ways to categorize things, and the categorization process can be quite subjective. In general, though, categories are used in order to make it easier to understand and think about large groups of objects or ideas.
For example, one might group all animals into a single category. Within that category, there could be further divisions based on characteristics like size (e.g., small mammals), diet (e.g., herbivores), habitat (e.g., aquatic creatures), etc. The more specific the categories become, the easier it is to compare and contrast different items within those groups.
Categorization can also help us notice relationships between things we might not have seen otherwise. For instance, putting all the animals together in one group may help us realize that they share certain features (like fur) while other objects do not. This understanding can lead to new insights about how these items fit into our world.