SL: Satellite link, I believeFor those (like me) who are unfamiliar with all the telecom acronyms:
NGSO - Non Geostationary Orbit
FSS - Fixed Satellite Service
CIR - Committed Information Rate
SLA - Service Level Agreement
VSAT - Very Small Aperture Terminal
SL - unknown
ISL: Inter-satellite link
LISL: Laser ISL
(on edit: aced by @mongo by a fraction of a second!)