Design Patterns
Patterns are higher-order designs, which occur repeatedly in object-oriented design. They have been formalized, and are generally considered a good development practice.
Refactoring
Refactoring is a disciplined technique for restructuring an existing body of code, altering its internal structure without changing its external behavior.
UML
Unified Modeling Language makes it possible to describe systems with words and pictures. Especially notable use case diagrams with their stick figures or the widely used class diagrams.
Git
Git is a backbone of modern software development. It is a distributed version control system that allows multiple developers to work on a project simultaneously without conflicts.