X IS...

X marks the place where the treasure is hidden
X indicates what is forbidden
X is a kiss
X is a Miss
(the one that was cited in my divorce)
X is for hope when predicting your draws

X shows where to sign your name
X matches O in an old childhood game
X is the ray that shows up a bone
X leads the way on Moore's Xylophone

X is the brand that leaves washing soiled
X is the secret concealed in the files
X+ mas is a time of the year
Xx4 an Australian beer

X can mean scary
X can mean sex
Whatever it means
It's included in teXt.