Android Question FirebaseAuthREST class- What is a oobCode?

[Paolodc]

Sorry guys in this tutorial is explained how use the methods for sign up/ sign in with email and password in my own Firebase project.

https://www.b4x.com/android/forum/threads/b4x-firebase-auth-rest-api.119935/#content

Between all of them there are particularly one that I didn't understand:

Public Sub confirmEmailVerification(oobCode As String) As ResumableSub
    Dim url As String = $"https://identitytoolkit.googleapis.com/v1/accounts:update?key=${API_KEY}"$
    
    Dim json As JSONGenerator
    json.Initialize(CreateMap("oobCode":oobCode))
    
    Dim j As HttpJob : j.Initialize("",Me)
    j.PostString(url,json.ToString)
    j.GetRequest.SetContentType("application/json")
    
    Wait For (j) JobDone(j As HttpJob)
    Return GenerateResult(j)
End Sub

What is the oobCode ? In the Firebase forum is very difficul search the documentation about it.
Please, Are here someone who can explains what is it and how custom it, or at least where find the complete reference?

Thanks you for all!

PS: Sorry for my english!