Semi-dedicated gives you the best of both worlds between a dedicated server and a shared server. Dedicated servers are fast but expensive; shared servers are cheap but slow (because many sites share the same CPU and RAM).
Semi-dedicated is technically a shared server, but instead system resources like RAM and CPU are allocated dynamically in blocks on the fly. Our system automatically allocates these movable resources wherever and whenever it's needed.
We deploy this system on all our packages. Even our most basic hosting package 'Essentials' guarantees a minimum of 1 GB RAM and 1 CPU core just for your website. This is not possible with traditional shared hosting and would be extremely expensive on a dedicated system.