If you invite someone to your organisation (or someone else does), you'll see their name in the list on your Organisation page. You may find that you've mistyped their address, or perhaps they no longer need access. For security, it's best to revoke (i.e. remove) invitations that are no longed needed.
Visit your Organisation page and find the list of invited users by scrolling down.
To remove an invitation, click the red "Revoke" icon on the right-hand side of the row containing the entry you want to remove. The invitation will be revoked (which means the person with this email address can no longer create an account), and you'll see a green notification at the top right of the window confirming that this has been done.