Hello!
I have this in mysql.user:
mysql> select User, Host, Password from user;
+----------+-----------+------------+
| User | Host | Password |
+----------+-----------+------------+
| root | localhost | *Password |
| root | dhcppc0 | *Password |
| root | 127.0.0.1 | *Password |
| username | localhost | *Password |
+----------+-----------+------------+

But I don't understand what host is the dhcppc0 in the table. What is it its origin/use?
Also, can I safely remove username@localhost, root@dhcppc0 and root@localhost?
Thank you!

It's your machine's name. You can revoke the permissions (using revoke) or simply delete the record in the user table.

//Edit
Keep root@localhost and username@localhost. Use root for maintenance (inserting / deleting / updating records is not maintenance) and use other users with finetuned permissions to use the database.

I once hosted a website somewhere and had three levels:

• a user that could create / delete databases and tables; on my own server this is root that can also provide the grants on the cerated databases / tables
• a user that could select / insert / update / delete records etc
• a user that could only select

Thank you!