what does 2300 on bill indicate

2300 text seems to be when you text in a group text , instead of listing all the participants in that thread, the text 2300 is inserted. We have several different family multi person threads. When I check the call log, only one or two numbers from that thread is on the log and the text 2300 is there instead of all included numbers from the thread. It seems to condense the rest of the included numbers to 2300 instead of listing them. I am shocked by how clueless T-mobile is to be able to give its clients an explanation.