Colocation server hosting means storage of your server at a facility of a third party service provider. A colocation service provider facilitates you with an Internet connection for your server and allows you to physically access your server whenever required.
On other hand,
dedicated Server is a server offered by a web host on rent. You can only remotely access your server and according to your varying requirements configure the server. Ideally speaking, the server is owned by third party web host and you can’t physically access to the server.