While a remodel changes the shape of something (like adding a new shower to an existing bathroom), a renovation focuses more on restoring something old so that it's in good shape (for example, fixing a creaking floor). Remodeling is much more profound than renovation, since it involves restructuring or changing something drastically. For example, adding a shower to a bathroom that didn't have one before would be a remodel. Another example would be to build a deck or add an addition to your house.
These are larger projects that can dramatically affect the structure or utility of the room. These should always be left to professionals. While remodeling is more expensive than most renovation projects, it's simply unavoidable under certain circumstances, especially when you're building your dream home. Renovation and remodeling may have different prices and requirements and take different periods of time.
Renovation and remodeling are two drastically different types of home design projects, but both can be useful in creating the home of your dreams. You've probably seen a lot of construction and design websites talk about remodeling and renovation, but you probably think that these terms are interchangeable.