A Few More Terms

Denial of Service (DoS) - an attack that only allows the attacker to inhibit a service, without gaining anything else.
"Owning" a machine - achieving the same (or higher) level of control over an attacked machine as the legitimate administrator of the machine.
Root kit - a set of files and utilities the attacker leaves on the cracked machine, to allow easy re-entry, or to collect information not otherwise immediately available.

Denial of Service (DoS) - an attack that only allows the attacker to inhibit a service, without gaining anything else.