The ##BEFORELAST formula refers to a function designed to extract or manipulate a portion of a string based on the position of a specific delimiter, focusing on everything before the last occurrence of that delimiter.
Example:
##BEFORELAST('Here we are', ' ') will return 'Here we'
Example:
The field name consists of ' Samuel Worobel'.
##BEFORELAST("Name",' ')
It will extract the first name ( Samuel) from a full name where the last name is separated by a space. If there were multiple spaces, only the text up to the last space would be returned.
Then, if you only need to retrieve the last name, you can use the function Last().