When an algorithm reaches a(n) operation, it waits until someone or something provides it with a
value.
computational
arithmetic
input
output

The answer to this question is input operation. Input operation is the signals/data that received by the programs to start a certain operation.
In personal computers for example, input operation needs to be triggered by the computer users that click the icon on the screen or type something through the keyboards.

Answer the car to the left must yield the right of way to the vehicle on the right;