AFAIK – As far as I know
BIS – butt in seat miles
DBC - denied boarding compensation vouchers
DO - officially a gathering of 12 or more at an event intended for FlyerTalkers. In reality, a gathering of any number of people involving large amounts of alcohol!
eVoucher – special upgrade voucher for use on M&M integrated partners
F or F class refers to First Class.
FCL - First Class Lounge, both in FRA and MUC
FCT - the First Class Terminal in Frankfurt
flat-bed seat - horizontal sleeper seat
FRA – LH’s main hub in Frankfurt
FTL – Miles and More Frequent Traveller Status
HON - is the highest M&M status (600k miles within two calendar years on M&M integrated partner airlines only)
HON RUN® - special European mileage run in premium cabin, see below
IIRC - If I recall correctly
LH – Lufthansa
lie-flat seat - flat seat but at an angle (not horizontal)
LO – LOT Polish Airways
LX – Swiss
MUC – second main hub in Munich
OS – Austrian Airlines
OLCI - Online Check-In
Op-Up - Operational Upgrade (free upgrade given for no specific reason)
PNR - Passenger Name Record
RTW - Round the World ticket
SEN – Miles and More Senator Status
SSSS - Selected for Secondary Security Screening (printed on selected boarding passes usually ex-USA meaning you're going to get extra screening by security)
TATL – TrAnsaTLantic (as in a ‘TATL trip’)
ZRH – LX hub in Zurich