A one-time filing in Form 720 (Quarterly Federal Excise Tax Return) refers to the initial filing by a new taxpayer who has recently become liable for federal excise taxes. This filing establishes the taxpayer's account with the IRS and sets up the reporting schedule for future quarters. A regular filing, on the other hand, is the periodic filing of Form 720 by established taxpayers to report and pay the federal excise taxes for the previous quarter. The frequency of regular filings depends on the taxpayer's reporting schedule, which can be monthly, quarterly, or annually.