Hi@Shashi,
The declarative pipeline is a relatively new feature that supports the pipeline as a code concept. It makes the pipeline code easier to read and write. This code is written in a Jenkinsfile which can be checked into a source control management system such as Git. Whereas, the scripted pipeline is a traditional way of writing the code.
You can also go through the below link.
https://www.edureka.co/community/54705/difference-between-declarative-pipeline-scripted-pipeliine