Semantically related keywords allow you to find keyword phrases that often appear along with the base keyword you typed in. For example, if you type in "lenses", you will find Keyword Strategy Studio suggesting semantic keywords like...
As you can see, semantic keywords are very useful in identifying subjects and fields that are closely related to the main base keyword.
Since the software finds these keywords from the web, the suggested semantic keywords will change if you repeat the lookup after a few hours.