There are some big sites that have to manage data for a large number of users or consumers. Sometimes the users find that the site becomes slow and less responsive. In many cases, this is not a system problem but it is sabotage being done by some criminal online experts who attack the site and affect its applications and alters them and makes them less efficient. These attacks are known as application-level distributed denial of service (Application DDoS). It is known by some other names also like 'low and slow attacks', 'layer 7 DOS attacks', and 'asymmetric attacks'.
This problem has been encountered in the companies and many solution providers have emerged on the internet to help the companies to fight these mischievous attacks which slow down the working of the company site and affect it in many ways.
There are many such solution providers including one that you have mentioned in your query.
Some of the reputed DDoS protection service providing companies are - Cloudflare, Imperva Incapsula, Arbor DDoS, Kentik, A10 Thunder, Radware DefensePro etc.
Knowledge is power.