What is the intermediate state before birth (Gandhabba)? What is the intermediate state before birth ("Gandhabba"), mentioned in some Buddhist traditions?

I have only heard the word so I can't explain the question any further.

I would like a detailed description of it if possible.
As far as I know, Theravada Buddhism refuses an intermediate state and says that a new life begins right after the death of a being. Although I have heard the theravada buddhist monk Ajahn Brahmali, mention in one of his videos, that there is an intermediate state.
So maybe there are different views on this topic, within Theravada Buddhism. Anyway, be careful about limiting yourself, to one tradition regarding this topic. No one really knows what happens in this stage, unless one has reached the necessary levels of insight, supernormal powers or enlightenment.
In Tibetan Buddhism, we have descriptions of the intermediate states between death and the beginning of a new life. The in-between-states are called Bardos. I remember reading about them in the &quot;Tibetan Book of Living And Dying&quot;.
This is an amazing book, that I think every Buddhist should read, no matter what tradition one follows. This book is filled to the brim with pearls, treasures, insights and jewels.
Here is a quote from the book, on the Bardo of Becomming:

THE DURATION OF THE BARDO OF BECOMING
The whole of the bardo of becoming has an average dura- tion of forty-nine days and a minimum length of one week. But it varies, just as now some people live to be a hundred years old, and others die in their youth. Some can even get stuck in the bardo, to become spirits or ghosts.
Dudjom Rinpoche used to explain that during the first twenty-one days of the bardo, you still have a strong impression of your previous life, and this is therefore the most important period for the living to be able to help a dead person. After that, your future life slowly takes shape and becomes the dominant influence.
We have to wait in the bardo until we can make a karmic connection with our future parents. I sometimes think of the bardo as something like a transit lounge, in which you can wait for up to forty-nine days before transferring to the next life. But there are two special cases who don't have to wait in the intermediate state, because the intensity of the power of their karma sweeps them immediately on to their next rebirth.
The first are those who have lived extremely beneficial and positive lives, and so trained their minds in spiritual practice that the force of their realization carries them directly into a good rebirth. The second case are those whose lives have been negative and harmful; they travel swiftly down to their next birth, wherever that might be.
-- Tibetan Book of Living and Dying, p. 295

I would suggest that you read the entire chapter &quot;Bardo of Becomming (p. 291)&quot;, but also the chapter &quot;The Process of Dying (p. 248)&quot;. The entire book is highly recommended but also takes a lot of time to read. So pick and choose if your time is limited.