Speed and reliability testing (load / stress / performance testing).
This test helps to check a behavior of websites (or its parts) at the same time with an influx of a lot of users. Poor performance (speed) - this is the main issue of many Internet projects.
You can build really cool useful site, but low performance could decreased all your achievements.
Performance testing can answer on questions such as:
Speed/Performance: How quick a respond to application after beginning of testers request?
Scalability: Is application performance always changing dramatically depending of the number of testers?
Stability: How stabile your system during sudden changing of queries quantity?
Confidence: How long the site can withstand the load of large quantity of requests which targeted on your site?
So, don't forget about checking the performance on your site/app - it is allow you to save money for future improvements, for instance - SEO.
I want to suggest you one good tool which can help you:
Enjoy your site performance!