CTR is the number of clicks on your CTA button, versus the total visitors to that landing page or ad. If 1000 people visit your landing page/view your ad, and 650 people click on the CTA, your CTR is 65%. A high CTR depends on a number of factors, chief among which are the value proposition on your page/ad, your CTA’s placement, and the relevance of your content vis-à-vis your target audience.
Lead generation falls within the second stage of the inbound marketing methodology. It occurs after you've attracted an audience and are ready to convert those visitors into leads for your sales team (namely sales-qualified leads). As you can see in the diagram below, generating leads is a fundamental point in an individual's journey to becoming a delighted customer.
Over time, the popularity of email marketing campaigns resulted in personal email inboxes that were overflowing with the latest and greatest offers. Email campaigns grew and people grew tired of them. Laws that allowed customers to unsubscribe breathed new life into email marketing campaigns as customers could easily pick and choose the companies they were interested in.