Most implementations of cucumber can automatically replace parameter values with some run time value. Let say in your feature file you want to write steps like this:

Scenario: MyScenario
    When I print 'Hello from test case {test}' 
    When I save the value '{test}' to my database

Then you might be tempted to write these bindings (dont do this…keep reading!)

[Binding]
public class MyBindings
{
    [StepDefinition(@"I print '([^']*)'") ]
    public void PrintMessage(string Message)
    {
        string Name = ....
        Message = Message.Replace("{test}",Name)
        Console.WriteLine(Message);
    }

    [StepDefinition(@"I save '([^']*)' to my database") ]
    public void SaveToDatabase(string Message)
    {
        string Name = ....
        Message = Message.Replace("{test}",Name)
        Console.WriteLine(Message);
    }
}

This way of writing step definitions becomes a real problem as the size of your automation increases:

1. we have to repeat the same logic in every step definition.
2. Its easy to forget to repeat that code.
3. New placeholders need you to find and update all places where this kind of parsing is done.
4. Its code that’s needed but not relevant for the objective of the step definitions.

Luckily SpecFlow’s Step Argument Conversion helps us! We can simplify our binding code to this:

[Binding]
public class MyBindings
{
    [StepDefinition(@"I print '([^']*)'") ]
    public void PrintMessage(string Message) => Console.WriteLine(Message);

    [StepDefinition(@"I save '([^']*)' to my database") ]
    public void SaveToDatabase(string Message) => Console.WriteLine(Message);
    
    [StepArgumentTransformation]
    public string TransformParsedString(string input)
    {
        string Name = ...
        return input.Replace("{test}",Name);
    }
}

Other implementations of cucumber also implement this principle. Its frequently referred to using these buzzwords:

1. Transforms / Transformations
2. Parsing / Replacing
3. StepArgumentTransformation