When you pay for traffic (visitors) that click on your advertisements that are being advertised on search engines, this is called pay-per-click or search engine advertising.

Paid search allows you to quickly leverage search engine traffic by bidding for keywords that are related to the products or services that you promote and sell on your website. Paid search advertising is particularly beneficial to companies who are not yet well ranked on search engines through natural search.

Benefits of Paid Search Advertising:

Can achieve top ranking through paid search if not ranking through natural search
It’s non-intrusive as you are reaching people when they are actively looking for information about your products and services online
Send targeted visitors directly to your offering on your website
Increases brand awareness
Keeps your competitors off the pages
It’s scalable and controllable and you only pay when people click on your
You can appear on search engines almost immediately
You remain top of mind

How Google Adwords works