AKB48 is a group of many females singer... and they are not permanent members... they have many members come and go in past until now...
Its like you learn singing in this group and you get better and "graduate" from this group then next generation go in... like morning musume...
actually their voice, dancing and stage skill is better than the korean group (i forgot any of the korean group name)... korean is using "sexual dancing way" in stage to draw attention...
AKB48 have many sister group... JKT48, TPE48, SKB48, SDN48, NMB48, HKT48, SNH48, and many more... btw AKB means akihabara... 48 means the group president's office name "office48" so it became AKB48...

SKE48 = Sakae
SDN48 = Saturday Night (its more adult version)
NMB48 = Namba
HKT48 = Hakata
JKT48 = Jakarta (yes. Jakarta Indonesia. The first AKB48 sister group from outside Japan. Members are indonesia young singers...)
SNH48 = Shanghai (yes China also got)
TPE48 = Taipei (Even asian one of top entertainment country also build one)

the best thing ever on this group... japan give them 1 theater called AKB48 theater... where do you find a pop group that has their own theater to perform? no right?

and lastly... AKB48 now is currently the world biggest pop group... Guinness World Record confirm it with 88 group members that make them is the world most pop group members on a single group (AKB48)

Laugh?? Japanese girls (i am not sure which one. too many online dancer) made something incredible... their dance hit on the game producer and they create a dancing machine based on them... i forgot the name of that arcade machine... i think is maimai... you laugh at her? they laughing louder while earning money...

Well... some of them really can meet outside activities... sometimes my jap frens told me they go to arcade center for play dancing arcade ^^