To resist is to well, resist. There are various things that can mean a resist. Basically, what would of been a "saving throw" in EQ1, is now to resist, except now it's to normally completely shrug it of. You can increase your resistances by certain pieces of armour, certain racial abilities, and some skills. Some skills say "resistability increases vs. lvl higher then lvls...." This means if it is over the lvl it says, it has a much better chance to resist. Some skills like Harm Touch are very hard to resist.