In theatre, an initialism for "Lights." Typically called by the stage manager with a number denoting the cue number to be executed by the lighting board op.
Stage Manager: Stand by LX 34 through 38.
Board Op: Standing by.
Stage Manager: LX34 go.
Board Op (after the cue's fade time is over): Complete.
Text-messaging abbreviation for "linguistics".
y r u l8 4 lx class?
Pretty much the "fetch" in Mean Girls in replacement of "xo" or something else slightly more normal (despite however much cringe-worthy).
Basically what dweebs say because they're trying to make up a new abbreviation that will never be cool because,
a) They're the only ones saying it.
b) No one knows what it means.
Lx", random post to a friend on Facebook that is both meaningless and dim-wittingly pointless.