Press embargos are when a company asks media outlets not to publish certain information until a specific date. Many startups that are riding in “stealth mode” will release information to reporters and agencies under a press embargo, setting up and helping to cultivate compelling stories before they make their product or company publicly known.
What this allows for is a burst of media activity when your company's news “goes live.” Your story can essentially be held on “standby” and released when you go out of stealth mode.
The advantage to you is that you aren’t waiting days, weeks, or even months for a news story. The advantage to the reporter is that their story gets to be among the first to be released. This helps build their relationship with you as you release more and more news.
Press embargos are often casual—a meeting with a reporter and a conversation about being tactical about the release of information for the advantage of both parties.
If your company is has this type of an opportunity coming up, and you're confident that your news will be exciting when it's released, it might be worth trying to set up a story by pitching a reporter the opportunity for an exclusive before you launch with a press embargo agreement in place.