Continuous integration

CI is DevOps practices where developers regularly integrate CODE with at regular time interval  The integration is accompanied by build and tests in an automatic way. The automated TESTING is optional in  CI but it is implied. The biggest advantage of CI is frequent integration which leads to early detection of errors and early remediation. We can work on CHANGES which lead to SPECIFIC build error or code issue. Since integration was frequent so fixing becomes easier.

Continuous delivery 

CD is the next step of CI so it can be considered as an extension of continuous integration which facilitates releasing new changes in the production environment in a controlled way. The code base has to always be in a deployable state to facilitate CD pipeline in DevOps.The continuous delivery ensures seamless delivery of any changes whether it be code /configuration in production. This is very useful for the complex system where several developers working on the same code base making it very challenging to ensuring code base in a deployable state. The advantages of  CD is early detection of production issue and quick fix for same.

Continuous DEPLOYMENT

This practice is one more step ahead of continuous delivery. The continuous delivery releases changes in production in a controlled way but continuous deployment facilitate the release of changes to production automatically once all changes pass through production pipeline stages successfully. It ensures no human intervention. The feedback loop is much faster if we enable continuous deployment for our project. It supports the theme fast to market. It is similar to continuous delivery but release happens seamlessly.