Here is a definition found on www.sos-homophobie.org :

“Coming out is the voluntary announcement of our sexual orientation or gender identity to our family or friends.”

The expression “coming out” comes from the verb “to come out”. But come out from where? The “closet”, a place where we hide our desires, where we retreat when we are scared of what could happen if we reveal that we are lesbian, gay, bi or trans. In someone’s life, coming out is a very important moment. It is a decisive step in accepting ourselves. Each person remembers the day where they told their parents, their friends, their brothers or their sisters that they feel attracted to someone of the same gender.

It is a very courageous act, a moment where we are vulnerable and that we are often brought back to when we talk about ourselves. Coming out can happen nicely, but it doesn’t always happen as easily as we hoped it would. We don’t always choose the “right” moment – but is there a right moment? We have to surround ourselves well, in case we don’t get the reaction we expected, so we are not alone.

What is called “outing” also comes from the same expression, but it is different from “coming out”, which is a personal and voluntary act. “outing” is the act of revealing that a person is homosexual without their consent. For the person that is “outed’, it is a violent act that can expose and weaken them.” (unofficial translation)

Revealing our sexual orientation is done in gradual steps that can vary in time, from one individual to another, and some will have to come out throughout their life if they want to reveal their sexual orientation or their gender identity to every new person they meet. Moreover, someone can choose to come out in one area of their life (e.g., friends) but not in another (e.g., family)

Sources:

SOS-homophobie, (s.d.). Qu’est-ce que le coming-out?, https://www.sos-homophobie.org/definitions/qu-est-ce-que-le-coming-out.