When Webhosting plans say "x visits monthly" what do they mean?

[Sebastian]

Are they only able to accommodate that amount of money on a monthly basis, or do they cut you off once you reach that limit?

Also, why is it measured on a monthly basis rather than by the number of people viewing your site at one time? Doesn’t that seem more relevant?

[Vincent]

It’s an approximate figure for the number of visits they can manage. Some hosts will not let you continue if you reach that threshold.