Aer Lingus calls them "Tier Credits", so as not to confuse everyone with BA's "Tier Points".

Your "Tier Credits" will expire at the end of your membership year.

Though, if like me, you have no status and therefore no card [other than the virtual Green card with no expiry date given] - there is no way of knowing when your year expires.

If you have a Tier Credits balance of zero, you can assume that your new membership year has recently started.