The term "cycle" is usually heard in Autosurf programs.

Lets say a program has plan of 8% for 18 days, one cycle of that program would mean the whole 18 days.

If you did "2 cycles" on that program, then that would mean you've been on that program for 36 days, thus 2 cycles.

Another example would be if an autosurf has a plan like 12% daily for 12 days, 1 cycle would be equivalent to the whole 12 days.

That's pretty much it. So doing 1 cycle means you've upgraded once, surfed, withdraw your profits, and when the last day of your upgrade/adpack has come, you did not respend anymore.