Neutralisation is where you make sure something is not too acidic are too alkaline. It’s very important in biology. For example, if soil isn’t neutral then plants can find it hard to grow. So you make it more neutral by adding certain types of ground up rock.
Neutralisation is when you either make an acidic thing less acidic or when you make an alkaline thing less alkaline. The acidic level of chemicals or things in biology can be very important for how they react with each other.