Wikipedia makes this distinction between "blocked" and "banned", which would be helpful to add to this discussion:
A block is temporary. It is used for preventing damage to the site by users who are editing maliciously. It can be applied to a user account, an anonymous IP, or a range of IP addresses. (source) Wikipedia admins may block users temporarily for vandalism, sockpuppetry (use of multiple accounts/IPs to circumvent the rules), and reverting others' edits to articles too frequently - among other reasons. They can present cases for longer-term blocks on the administrators' noticeboard or before the arbitration committee. Blocking is something one administrator can do as long as they are acting in accordance with admins' policies. Banning is, generally, a community process.
A ban is a measure taken against a user, designed to punish the user (and protect the site) as a result of actions they have done on the site (or sometimes offsite). On Wikipedia, users can only be banned by Jimbo Wales, the Wikimedia Foundation, the Arbitration Committee, or a consensus among the editing community. Some bans are of a fixed, long duration (e.g. one year) while others are considered permanent or indefinite. (source) Usually, bans take weeks/months to put in place unless the offenses are so severe that they need to happen much faster.
Among communities of forum moderators, "blocked" and "banned" can sometimes both mean "banned".