Efl
In short
The EFL Cup, currently known as the Carabao Cup for sponsorship reasons, is an annual knockout football competition for clubs in the top four tiers of English football.
In plain words
It is a tournament where teams play against each other to be knocked out until only one winner remains. It includes teams from the Premier League down to League Two.
A simple example
A small team from the third division might play a match against a massive club from the Premier League to try and progress to the next round.
Why it matters
It provides smaller clubs a chance to win silverware and play in major matches. It also offers a way for top teams to test younger players.
Easy to mix up
Do not confuse it with the FA Cup, which is a different knockout competition with a much longer history.