Cucumber is an Open Source test automation tool which supports Behavior Driven Development(BDD) and it is used to write acceptance tests for the different application.
It allows automation of functional validation in easily readable and understandable format (like plain English) to Business Analysts, Developers, Testers etc.
Companies often have huge issues with trust—the customer doesn't trust the supplier, the business doesn't trust the developers, the developers don't trust the testers, and the testers don't trust anyone. Cucumber gives the business, developers, and testers a way to collaborate and specify, in plain English, how the system should work.