Landlocked means "does not have a border that is a seafront". There's some opinions about it, but that's the definition. And for the curious a sea is a part of

Landlocked means "does not have a border that is a seafront". There's some opinions about it, but that's the definition. And for the curious a sea is a part of the ocean, by some geologic definitions including seabed and salt water, even if it becomes closed off, and a lake never was part of the sea.