You want to export a single content-type definition so you can import it again elsewhere.

1. Go to App Management > App > App-Settings and then click on export part 
2. If you're doing an export of a hidden content-type in another schema, switch schemas first - usually you don't need to do this
3. Select the content type (or types) you want to export. Choose only the top nodes, as in this example we're not exporting data, only the type-schema. Then scroll to the bottom and hit export. 

You now have an XML file containing the schema (field-definitions) of a content-type.