In C18 & C19 the Ton referred to the upper classes/ nobility living in London. As they were rich, they didn't have to work, so they mainly went to London parties & to the city of Bath in summer. The word is often used in historical romance novels., eg Mills & Boon. The novel's plot usually has a son of a noble family who are well respected by the Ton of London. He then falls in love with a poor girl, who ends up being the long lost daughter of a Duke who didn't care for London society. I hope that this helps you.