If this button appears in your list it means that you can cancel the Booking (this requires a license enable by e-GDS and it only works with Bookings that were made in your e-GDS B2C Booking Engine).
Here you can check in more detail all the information related to the booking you choose before.
You can enable (it only works if you enter your login "User Name" and "Password") also the "Card Details" in the button "Show card details" if you need to check or validate the client credit card.