This means the server you connect to sees all your activities and your IP address so it can create a link between your addresses, your IP, etc.
When you run your own Electrum server and connect to that instead, you solve the privacy problem I mentioned above since you are connecting to your own server and it is a full node so it is connected to other full nodes and is relaying transactions like any other node so nobody can create the link between your addresses or your transaction and your IP address.