No, it means that "enough people have been infected that each new infection causes less than 1 infection." Lets say we're in the middle of an outbreak and reac

No, it means that "enough people have been infected that each new infection causes less than 1 infection." Lets say we're in the middle of an outbreak and reach herd immunity. The infected people are still going to infect others, just less than the number currently infected. And then those people go on to infect an even smaller number. And so on. This is called "overshoot" and can end up being a significant number of people. One of the reasons for the "flatten the curve" heard immunity strategy is that it limits overshoot as well as reducing strain on medical facilities.