A remote development environment usually refers to a developer working on their desktop machine and running software that enables them to replicate the running environment of the server so they can test code without uploading it to a server.
Very often to test the full functionality of the SaaS system, especially to test how the system is affected by the load of many users, the developers have to test on the main server. But it is substantially faster to write code locally (meaning on your desktop or laptop) than it is to upload every time a line of code needs to be seen operating.
Setting up a remote development environment can be a time consuming task, especially if the developers initially setting everything up didn’t document their work. However, there are systems available that make this task a lot faster such as Docker and Vagrant. Your lead developer will determine which remote development deployment system to use.