The obj folder holds object, or intermediate, files, which are compiled binary files that haven’t been linked yet. They’re essentially fragments that will be combined to produce the final executable. The compiler generates one object file for each source file, and those files are placed into the obj folder.

The bin folder holds binary files, which are the actual executable code for your application or library.

source: https://stackoverflow.com/questions/5308491/what-are-the-obj-and-bin-folders-created-by-visual-studio-used-for