3-TIER ARCHITECTURE
A 3-TIER ARCHITECTURE is a type of software  architecture which is composed of 3 "tiers" or "layers" of logical computing. They are often used in applications as a specific type of client-server system. 

What Do the 3 Tiers Mean?

• Presentation Tier- The presentation tier is the front end layer in the 3-tier system and consists of the user interface. This user interface is often a graphical one accessible through a web browser or web-based application and which displays content and information useful to an end user. This tier is often built on web technologies such as HTML5, JavaScript, CSS, or through other popular web development frameworks, and communicates with others layers through API calls.
• Application Tier- The application tier contains the functional business logic which drives an application’s core capabilities. It’s often written in Java, .NET, C#, Python, C++, etc.
• Data Tier- The data tier comprises of the database/data storage system and data access layer. Examples of such systems are MySQL, Oracle, PostgreSQL, Microsoft SQL Server, MongoDB, etc. Data is accessed by the application layer via API calls.