A computer simulation was a simulation performed on a computer to help predict results.
In 2259, a computer simulation aboard USS Enterprise suggested that the comet C/2260-Quentin striking the M-class planet Persephone III would leave no survivors. (SNW: "Children of the Comet")
In 2370, Ensign Taurik asked Geordi La Forge to look at a computer simulation he was running in engineering to test a new warp field configuration. La Forge noted a problem with the simulation, in that the plasma flow to the nacelles was out of sync. Taurik had done that deliberately as the configuration increased overall warp field integrity by seven percent. Taurik then stated that Doctor Nils Diaz had been experimenting with the same technique at the Tanaline Propulsion Laboratory. Taurik requested to begin tests to see if the technique could be adapted to the USS Enterprise-D's warp drive, but was denied over variables that he may not have accounted for. La Forge would have to see the simulation before he authorized any tests. (TNG: "Lower Decks")