Terminal Guidance - allows refinement of target position, etc. before hitting, mainly after midcourse guidance. I.e. the R-77 is actually guided (SARH) before its own seeker turns on.
target memory - Remembers what target it is, and good for AAMs and Anti-radiation missiles
mid-course correction - Mainly for AAMs, the radar updates the missile mid-flight.
home on jam - self-explanatory, so when the aircraft jams, it's not fooled and switches to home on the jammer of the targeted aircraft.
optical back-up - Has an optical seeker (radar AAMs) as a backup to it's primary sensor.
IFF interrogator - determines if it's a friend or foe, but seems to be borked in TW sims.
seeker uncage - lets the seeker track the target
seeker slave - Mainly for helmet mounted sighting systems, the seeker follows the monocle on the helmet.
sea skimming - pretty self explanatory.
terminal pop-up - before hitting the target, it rises up before hitting the target.
lofted - "lifts up" when launched.