I bought some extract for dessert making and got the blossom water on a whim, since it was right next to it on the shelf. The blossom water smells a little sharper, but they both taste the same straight and I haven't played around with them enough to get a gut instinct on which one goes in what. What's the base difference between the two and how they're used?
Orange blossom water is distilled from actual orange blossoms, and will have a subtle orange flavor, probably more delicate and complex than orange extract, at least on a per volume basis.
Orange extract comes from the zest or colored part of the fruit, and is a very powerful flavoring with a strong orange presence, but no acidity.
You will find that blossom water is more commonly used in recipes from the middle east and northern Africa, that have migrated up into Italy and France as well.
Orange extract is used in more assertive, more typically western recipes.
Given that fresh oranges are readily available, and the zest can be removed and use directly, using either of these is not as common as it otherwise might be.