Search Engine Optimisation is a direct investment in your visibility and profitability as a company. It brings visits to your website or buys you more visits to your website. No matter what your business does, it is important as search engines are developing, it's highly unlikely that SEO will lose importance any time soon.
Pay-per-click, is the cost per click onto your website. It is an internet advertising model that buys visits to your site. It is used to direct traffic to websites, in which an advertiser pays a publisher when the ad is clicked.