It means that whilst you might catch it and spread it, then the rate of spread will be lower so you might be able to spot an emerging cluster.They just had a Sir Prof on BBC. He said that if the UK can reach 60% herd immunity all restrictions could be lifted but did say that they can't tell how high it is. He wasn't advocating it just explaining the interest in this aspect. Afraid I can't see how this can mean that there aren't still some infected people about. He also mentioned that lock down is unlikely to change for weeks and relaxations could only be slight without considerable risk.
60% would require a vaccine, in which case it's only a stepping stone to higher numbers, or a huge death toll.