In general, the X just means it was outcrossed.
Not sure exactly what AGS is sending out as freebies but some shorthand-
NL=nothern Lights
WW= white widow
X= cross (it's an F1 hybrid)
IBL= inbred line (stable)
F2= 2nd generation hybrid, much phenotypic variation, good for choosing the perfect mother
BX=backcross, taking an F2 or F3 hybrid, picking the perfect pheno, and then backcrossing it to one of the original parents of the hybrid to stabilize
uh....there's more but I'm not bored enough to post them atm lol.