What is the X in X-mas?
1934, initialism for extra-sensory perception.
1. Extra Simple Pascal. Subset of Pascal.
2. Econometric Software Package. Statistical analysis of time series. "Econometric Software Package, User's Manual", J.P. Cooper, Graduate School of Business, U Chicago. Sammet 1978.
3. Extended Self-containing Prolog.
4. An early symbolic mathematics system.
[A. Rom, Celest Mech 3:331-345 (1971)].