Finishing salts is a generic term for salts that have a special crunch, colour or flavour that would be lost if you added the salt into a dish as an ingredient as part of the general cooking process.
Instead, these salts are best sprinkled on food just before serving in order to preserve the special qualities of the salt for your guests to appreciate.
An exception would be in barbequing: finishing salts can often be pressed into items such as the skins of potatoes before barbequing, as the salt will both stay there and still be accessible for appreciation when eating. Don’t do this with meat or skinned fish, however, as the salt gets absorbed into the flesh.
Using such salts for “finishing” purposes is also very practical, given what such special salts usually cost.
While most people think French sea salts when they think finishing salts, as more and more people come to taste Maldon Sea Salt, the Maldon salt is often preferred.