Tolerates seaside conditions.

This generally refers to salt spray, but in includes high humidity and almost no seasonal differences.
If the wind blows from the sea on a regular basis and you live within a mile or two from the breakers you can have salt spray making it to your garden. With the salt comes sodium that can burn plants that do not tolerate sodium.  Black leaves or brown-black leaf margins are common.
High humidity doesn't seem like a problem unless you are a plant adapted  to only occasional rain. Mold, bacteria, drowning all happen to some interior plants when they are planted next to the coast.
No frost is a problem for plants that need frost to tell time. Some plants either do not go into or come out of dormancy. A plant with three leaves on it that look like they need to fall off all year  is not a good looking plant.

So some desert species tolerate the salt and the humidity can grow next to the sea, like Bladerpod. Some interior plants seem to do well there, like Hummingbird sage. But most do not want to be there and let it be known by dying.
If you know a plant will grow in seaside conditions, fine, otherwise use plants that grow native in your area.