What does the "module not found error can't resolve 'popper.js'" message signify in a development environment?

This error message indicates that your build tool (commonly Webpack, Parcel, or similar bundlers) cannot locate the 'popper.js' module that one of your project's dependencies is trying to import. It's a build-time error, meaning the bundling process failed because a required JavaScript module was not found in the `node_modules` directory or at an aliased path specified in your bundler's configuration. It often occurs when using libraries like Bootstrap that depend on Popper.js for functionality like tooltips, popovers, and dropdowns.