ban or block? 

As I understand it, a ban is something imposed on a user by the community appointed Arbcom or Jimbo Wales by fiat for whatever reason, and a block is something any admin does to an individual user account or IP address for predetermined reasons (usually vandalism, sometimes immediately if the vandalism is severe or offensive enough, or in the case of continued actions by users blatantly against policy in the face of multiple warnings). They can both be for a set time or permanent. Bans can be permanent, blocks of user accounts can be permanent, but we don't like to permablock IP addresses. As in the case of Jessica, I blocked (what I believe to be) her IPs for 6 mos., so it ever gets reassigned to another computer after that time that computer can conceivably register for a new user account. Known shared IPs are blocked for much less time. Admins are supposed to use Arbcom mandated block ranges to enforce bans, but don't themselves declare bans on other users in order to block or have other admins block. That way, admin actions can be reversed by other admins or even by themselves if they change their minds, but bans "from above" can't be lifted by admins. Again, this is only how I understand it, others will have their own opinions to be sure. Cheers,