There are two syntaxes to define Pipelines—declarative and scripted. Originally, the Pipeline plugin supported only scripted pipelines, but Declarative Pipeline syntax 1.0 was added in February 2017 with Pipeline 2.5. Both of these syntaxes use the same underlying execution engine to execute instructions.

A Scripted Pipeline allows you to define your instructions using a full-featured programming language called Groovy; because of this, you are able to be very expressive. The downside is that the code may be less understandable, and thus less maintainable.

The Declarative Pipeline syntax brings structure to the Pipeline, which means it's easier to check the file for syntax errors, provide linting help. But with Declarative Pipelines, you can only define instructions that are supported by the syntax.

Therefore, you should use the Declarative Pipeline syntax wherever possible, and fall back to the Scripted Pipelines only when there are instructions that cannot be achieved using a Declarative Pipeline.