Cucumber is an open-source software testing tool written in Ruby that enables behavior-driven development (BDD) and facilitates collaboration between developers, QA, and non-technical participants. It uses plain English text to write test cases, serving as documentation, automated tests, and aid to development. Cucumber feature files help non-technical stakeholders engage with testing, while scenarios describe key actions and outcomes, using Given-When-Then structures. Step definitions are defined in Ruby files under features/step_definitions/*_steps.rb, reusing parameters to avoid hard-coded values. The Page Object Pattern is a superior reuse approach for step definitions, mapping UI elements to Ruby classes. Rspec-expectations library provides built-in matchers for testing validation. Cucumber configuration requires specific files, including cucumber.yml, Gemfile, Rakefile, and support/env.rb, which simplify command-line execution and environment setup. A complete test structure involves writing feature files, implementing step definitions, running tests with the cucumber-js executable, and using a simple "hello world" example to demonstrate its usage. Cucumber allows for team collaboration early in planning and development phases, automating only what needs automation at the UI level, and laying a test automation foundation that follows coding standards and design patterns.