X-IN stands for Ex-Interest
X-ON stands for Transmitter On
X-INT stands for Ex-Interest
X-GDS stands for eXempt from the General Declassification Schedule
X-PMGM stands for Extended Parametric Meshless Galerkin Method
X-MAS stands for Christmas
X-FROG stands for Cross-correlation Frequency Resolved Optical Gating
X-POL stands for Cross-Polar
X-FIST stands for eXperimental û Fire Integration Support Team
X-KISS stands for XML Key Information Service Specification