Definition
A model is a representation of a specific type of data in your application and the rules that govern it. If your business software tracks clients, projects, and invoices, each of those is a model. The model defines what information belongs to that type of record (a client has a name, email, and company), how records relate to each other (a client has many projects, a project belongs to one client), and what business rules apply (an invoice amount must be greater than zero). Models are where your real-world business concepts are translated into something the software can work with.
Why It Matters
Models are the foundation of any business application. They determine what data your system can store, how different records connect, and what rules are enforced at the data level. A well-designed set of models means your application accurately reflects how your business actually works. Poorly designed models lead to workarounds — fields that store data they were not meant for, relationships that do not match reality, and rules that have to be enforced manually because the system does not handle them. Getting models right early avoids expensive restructuring later.
Example
An agency builds a project management tool. They create a Client model, a Project model, and a Timesheet model. The Client model defines that every client must have a company name and a primary contact. The Project model links each project to one client and tracks status, budget, and deadlines. The Timesheet model records hours worked against a project. Because these relationships are defined in the models, the system can automatically show all timesheets for a project, total the hours billed to a client, and prevent a timesheet from being logged against a non-existent project.