Shift Left
A typical software development process is sequential (1970s-1990s): define requirements, analyse, design, code, test and deploy. In this process, testing happens towards the end. Problems uncovered by testing at such a late stage can cause costly redesign and delays. The idea of Shift Left is to involve testing teams earlier in the process and to think about testing at all stages of the process.
Shift Left Left Testing Test Driven Development Behaviour Driven Development Continuous Integration Continuous Deployment
Source: devopedia.org