Two new settings in a source calendar's Exclusions section keep events from being copied. Exclude by Status skips events marked Busy, Free or Tentative, whichever you select. Exclude Titles Containing skips events whose title contains any of the words you list, ignoring case.
They suit events that should not block time elsewhere: a standing placeholder invite, a hold marked Free, or a meeting you have only tentatively accepted. Tentative is offered for Outlook calendars and for iCal links published by Outlook, the sources that report it.
Both settings are part of Pro, like the other event filters. Copies of events that match are removed on the next sync.
What a copied event shows lists the other exclusions.