Relevance score is defined by how the audience is reacting to your ad copy. For instance, if the audience you are targeting selects the "hide this ad" option, then this leads to a decline in relevance score. A high Relevance Score means people like the ad copy, and they do not mind viewing the ad. But, this does not mean that they are clicking on the ad more frequently. When your Relevance Score is low, then that means people do not like the ad copy, and they don't want to see it again. Relevance score has no connection with CTR because that would mean the viewer clicked on the ad, which he/she did not.