Formal admission is the moment a company’s shares are admitted to trading on a stock exchange. It’s graduation day for an IPO. The paperwork is signed off, the shares are on the market, and everyone can join in.
In the UK, admission is usually announced first thing in the morning, often at 8am, on the day the shares start trading unconditionally. The prospectus will normally give the expected date well in advance.
It’s rare, but admission can be delayed or cancelled, for example if market conditions change sharply or a regulatory condition isn’t met. If that happens, any conditional trades are cancelled.
Formal admission is also the starting gun for other things, such as the clock on a lock-up period.
Related terms: Conditional dealing, IPO, Float