alpha69,
Pretty much as shown on the link provided by Captivep.
Avios
- is a "currency" that you can redeem on all sorts of things ranging from seat upgrades to hotel rooms
- you can "earn" Avios in a multitude of ways, but the most common are credit-card tie-ins, air travel, other people transferring Avios to you, you buying Avios top-up.
- if you're really lucky, when you complain to BA about something worthwhile they might throw a handful of Avios in your direction for "service recovery".
Tier Points
- is what decides where your rank within the programme (i.e. Blue, Silver etc.)
- you can
ONLY earn Tier Points by actually putting your bum on the aircraft seat and completing the flight .... that is, afterall, the very point of an airline loyalty programme !
- of the three, Tier Points are the ones you really need to worry about if you want to make full use of the loyalty programme !
Lifetime Tier Points
Is a fairly new concept, basically there to reward the airline's most loyal and frequent flyers. Its a bit like BA Gold Guest List, except you need a fair few more points to see the benefit of Lifetime Tier Points, which at the moment equates to you being given Lifetime Gold status after reaching a specific level.