‘Designer babies’ is the name given to babies that have been created a certain way (e.g. with greater intelligence or athletic ability). It isn’t possible to make designer babies like this, in fact it is actually illegal in the UK. However, this doesn’t stop us talking about this when we think about genetics and the impact on society.
In theory you could make a ‘designer baby’ by making an embryo and then testing the embryo to see what genes it has. You could then choose to keep the embryo with the genes you wanted.
At the moment it is only possible to do this if you want to actively avoid an embryo with a serious life threatening condition. So, families who have inherited conditions that cause their children to die might want to use this technology to ensure that their future children don’t have the same dangerous inherited condition. They have a set of embryos tested and then they choose to keep the embryos that are healthy.