CI/CD is a method to frequently deliver apps to customers by introducing
automation into the stages of app development. The main concepts attributed
to CI/CD are continuous integration, continuous delivery,
and continuous deployment. 
CI/CD is a solution to the problems integrating new code can cause for 
development and operations teams (AKA "integration hell").

Specifically, CI/CD introduces ongoing automation and continuous monitoring 
throughout the lifecycle of apps, from integration and testing phases to 
delivery and deployment. 
Taken together, these connected practices are often referred to as a 
"CI/CD pipeline" and are supported by development and operations teams 
working together in an agile way with either a DevOps or 
site reliability engineering (SRE) approach.