This content is now covered in Configure how users can create and send invites for others to join your community
We have improved the core invite system in Discourse 2.5 to add a new feature – Invite Links. 
Invite Links can be used multiple times and is not tied to an email. Only staff users (admins and moderators) can create multiple use invite links.
Creating Invite Link
Invite links can be created from /my/invited page by clicking on + Send Invite button → “Multiple Users” tab.
The default upper limit for “maximum redemptions allowed” is 5000, for staff. It can be adjusted via site setting invite_link_max_redemptions_limit.
For non-staff users, the limit is 10. The user limit can be adjusted via site setting invite_link_max_redemptions_limit_users.
Invite Link Listing
Existing invite links can be viewed at /my/invited/links page.
Redeeming Invite Link
Invite link can be redeemed by multiple users and at the time of redeeming invite the user provides email address and username. User also has the option to set Name and Password.
Once the user accepts the invite they’ll have to click the account activation link sent on their email address.
Also, existing users can also redeem invite links and if the user already exists, it will skip that part of the invite and continue with the ‘add to group’ and ‘redirect to specific topic’ part of the invite.
Tracking Redemptions
Invite link redemptions can be tracked on /my/invited/redeemed page.
Any feedback here is greatly appreciated! 