Provisional patent application
A cheap, unexamined US patent filing that keeps a date warm for twelve months while you make up your mind.
Since 1995 the USPTO has accepted provisional applications: no formal claims are required, they are never examined and they never become patents. What they do give you is a priority date and the right to stamp "patent pending" on the product. A full application must follow within twelve months or the lot lapses.
After the America Invents Act moved the US to first-inventor-to-file in 2013, getting a date on record quickly mattered even more, which is why startups often file one before a pitch. The trap is that protection covers only what's actually written in it – a hastily drafted filing protects a hastily drafted idea.