Fundamental

What is Backend?

The backend is the data and infrastructure that make your application work.

ref: Backend Development: key languages, technologies, features in 2020 | DDI Development (ddi-dev.com)

What is Backend Web development 

Web development is based on Frontend and Backend development, both are necessary for any functional website. The frontend is based on styling and interacts with users whereas the backend web development works behind the scenes and interacts with databases. There are several languages and tools used by developers to create an effective webpage

ref: Backend Web Development: Details & Required Skill Set (temok.com)