A denial of service attack is the use of ordinary queries or access rights to overload a program, processor, database or (especially) bandwidth-limited net service especially a web service, typically with crapfloods. This denies all legitimate users access to the web (e.g. a large public wiki) itself. It is very easy to overwhelm those services that have a fixed bandwidth limit - accordingly, any use of any automated bot to create superfluous traffic on such a site, e.g. use of any vandalbot, must be considered a deliberate denial of service attack, regardless of the claimed intent of its use: its effect is exactly the same: denial of service when the limited number of users or bandwidth is exceeded.
In most developed countries such an attack is considered a felony or at least misdemeanour. If the attack is against so-called critical infrastructure (which means any essential service including banks or utilities) it can be considered an act of terrorism. This has been strongly contested by those who consider there to be a strong line between information and living bodies.