Continuous Intake was an option when starting a new prison. When enabled you would always receive a random number of prisoners every day, which you may not temporarily stop. When disabled, you would still receive a random number of prisoners every day, but you could temporarily stop the intake of prisoners by going to the prisoner tab which is located under "Reports". When you set each prisoner "class" (low, normal, or high security) to closed, the intake of prisoners will stop. To once again start the intake of the different prisoners, you would simply go to the to the Reports tab again and set the closed classes back to open.
If you disabled the intake, the number of random prisoners may build up until you re-open the prison.
Continuous intake was removed in the intake revamp of alpha 30.