Sitecore Helix is a collection of recommended practices and conventions for the solution architecture of Sitecore product implementations.

These practices are based on principles of modular architecture (a.k.a. package design), which help you to manage dependencies in your solution in a way that creates more maintainble code.

Application of modular architecture will decrease the cost of change of your Sitecore solution, help you reduce technical debt.

which describe how feature and functionality in the solution relate to each other.
which control the direction of dependencies and thereby assure a manageable solution.
which define the isolation of features and functionality leading to greater discoverability and simplicity in the development process.

Sitecore Helix Architecture Principles