What's the function of externals in NitroOptions?

[gjssss]

Hello, I would like to understand the purpose of the externals property within the NitroOptions.

...
  noExternals: boolean;
  externals: NodeExternalsOptions; // <-- This
  analyze: false | PluginVisualizerOptions;
  replace: Record<string, string | ((id: string) => string)>;
...

interface NodeExternalsOptions {
    inline?: Array<string | RegExp | ((id: string, importer?: string) => Promise<boolean> | boolean)>;
    external?: Array<string | RegExp | ((id: string, importer?: string) => Promise<boolean> | boolean)>;
    rootDir?: string;
    outDir?: string;
    trace?: boolean;
    traceOptions?: NodeFileTraceOptions;
    moduleDirectories?: string[];
    exportConditions?: string[];
    traceInclude?: string[];
    traceAlias?: Record<string, string>;
}

It don't introduce in the docs (May Be?)