npm install is a command used in Node.js to install a package and any packages that it depends on. When run without arguments, npm install downloads dependencies defined in a package.json file and generates a node_modules folder with the installed modules. When run with arguments, npm install downloads specific modules to the node_modules folder. The package.json file dictates what modules will get installed in the node_modules folder. Its important that npm install is run in the same location as the package.json file. npm install can also be run in global mode, which installs the current package context as a global package. npm install can manage dependencies, and it generates a package-lock.json file that describes the exact dependency tree that was installed.