An IPO subscription is an indication that you’re interested in buying shares once they’ve been listed. Subscription rates can have a direct impact on the initial share price. IPOs are often underpriced to ensure that the issue is fully subscribed or even oversubscribed by investors.
Oversubscription means there’s more demand than the number of securities issued – the prices can be adjusted upwards, and you could be allocated fewer shares than you requested
Undersubscription means that the supply of securities isn’t fully met by the demand, often because the security is overpriced