"Apple Invites" will be an iCloud+ feature, according to the page:
To increase storage, use Apple Invites to organise events, and enjoy privacy features like HomeKit Secure Video, Hide My Email, and iCloud Private Relay, upgrade to iCloud+.
Apple's paid iCloud storage options, which start at $0.99 per month in the US, are largely referred to as iCloud+. Apple offers a number of extra benefits with iCloud+ plans at no extra cost, like HomeKit Secure Video and iCloud Private Relay. It appears that Apple Invites is the newest benefit to be made available.
In addition to a new Apple Invites app for the iPhone and other devices, Apple Invites will be accessible online at iCloud.com/invites.
The iCloud.com/invites page description states that Apple Invites will assist customers in planning birthday celebrations and other events:
Make online invites for birthdays, baby showers, graduations, and other events. Keep track of RSVPs, make shared albums, and send them right away via text or email.
With no restrictions on the number of events they may organise, extra fees, or advertisements, iCloud+ members will have complete access to Apple Invites.
Apple Maps, Photos, Music, and more will all be integrated with Apple Invites.