What does early bird discount mean?

Book your winter holiday 20/21 long-term in advance (until 31 August 2020) and you will receive a discount of up to 20% on the resort price (without flight). When which club opens in winter varies and can be found on the resort detail pages.
The discount is available in all TUI MAGIC LIFE resorts. The only difference is the amount.

How much is the early booking discount? And does it also apply to children?

20% early booking discount in the resorts Fuerteventura, Africana and Sharm el Sheikh

10% early booking discount in the resort Kalawy

The discount applies to the resort price of all travelers.

What is meant by early booking discount, early bird discount, early booking reduction? Are these different things? 

There's no difference.

Until when is the early bird discount valid?

The discount for trips in winter 2020/21 is valid for bookings until 31 August 2020.

How is the discount deducted?

The discount is already deducted from the price of the trip.

Does the discount also apply to resort stays without a flight or to offers from X-TUI?

The discount is granted on the resort price and therefore also applies to bookings without flight.
It doesn't matter whether you are booking via TUI D or X-TUI.

Information on payment can be found here.