From the dictionary
Sealant- any of various liquids, paints, chemicals, or soft substances that may be applied to a surface or circulated through a system of pipes or the like, drying to form a hard, watertight coating.
Adjective-–noun - a substance that causes something to adhere.
Physics . of or pertaining to the molecular force that exists in the area of contact between unlike bodies and that acts to unite them.
So when building a boat there need to be a clear understanding of what needs to be sealed and what needs to be adhered.
For example- Decking should be applied with a marine sealant because it is a non-permanent bond. You can rib it up and out. Additionally nearly everything after the main structure is completed should use a marine sealant.
Lets move on to adhesives. Adhesives provide a permanent bond. The sheer clamp, frames, and anything structural that you never ever want to come apart should use an adhesive.
This is simple terms, and I still don't quite know exactly what needs what, but I'll figure it out along the way. If in doubt, ask a professional. They like giving advice, but always get a second opinion as well. With that it's time for breakfast. I'm out. Have a good day, and get building away!