What is Cucumber, Gherkins, Spec flow

• What is Cucumber?

Cucumber is a tool that supports Behavior Driven Development (BDD). It offers a way to write tests that anybody can understand, regardless of their technical knowledge.
In BDD, whatever you write tests in Given-When-Then steps.

• Gherkin is the language that Cucumber uses to define test cases. 
• SpecFlow is Official version of Cucumber

Feature: Withdraw Money from ATM

    A user with an account at a bank would like to withdraw money from an ATM.

    Provided he has a valid account and debit or credit card, he should be allowed to make the transaction. The ATM will tend the requested amount of money, return his card, and subtract amount of the withdrawal from the user's account.

    Scenario: Scenario 1
        Given preconditions
        When actions
        Then results

    Scenario: Scenario 2