Hey, welcome to PC.
Rapid cycling means you have four or more episodes a year, and it is very common among kids and teens. Four or more could mean simply mean a manic (or hypomanic) state during january-febuary, then a normal state in march, depression in april, manic in may, normal in june depressed in July, and manic in august.
jan + Feb = manic
March = normal
april = depression
May = Manic
June = Normal
July = depressed
August = Manic

That is already four episodes, and considered to be rapid cycling.
It can be as mild as four episodes a year, to as severe as several episodes a day.