It seems that we should have a tag for "semantic security". I've seen a couple of posts in the last couple weeks that would qualify for that tag, and semantic security is more than just about chosen plaintext attacks (which already has its own tag) since semantic security has different meanings in different contexts. Given that it's a fairly common term and fundamental to crypto theory, it seems like we should have a tag for it.
This sounds good, do it!
Given that you have already more than 150 reputation (which is what is needed to create tags), you can create the tag by simply adding it to the relevant questions.