Apple Ipad Rejoins Wlan in very short intervals

[vineet_tomar]

It's been observed that i am getting below message on ZD monitor tab for One of the client complaining about frequent disconnections.
User[8c:fa:ba:cd:89:c4] joins WLAN[MARKETCITY] from AP[Leasing and Marke]
2015/07/03 12:53:32
Low
User[8c:fa:ba:cd:89:c4] rejoins WLAN[MARKETCITY] from AP[Leasing and Marke]
2015/07/03 12:53:07
Low
User[8c:fa:ba:cd:89:c4] joins WLAN[MARKETCITY] from AP[Leasing and Marke]
2015/07/03 12:51:54
Low
User[8c:fa:ba:cd:89:c4] rejoins WLAN[MARKETCITY] from AP[Leasing and Marke]

What is the rejoin means why it's disconnected