IRstuff, I think that would be a helical gear, but maybe I don't understand what you are saying.
I would put the difference at size and use. If I had to put a hard definition on it, I would say a gear has a face width less than the pitch diameter and is intended to contact a rack or another gear using a portion of the teeth. A spline has a face width greater than or equal to the pitch diameter and is intended to contact another spline of the opposite gender using most, if not all, of the teeth.
Splines are for transferring rotational motion along the same axis.
"Involute" is a curve shape, basically what you get when you unwind a string from a spool and trace the path of the string's end. This shape has useful properties for transferring motion.
The spline involute is the same as a gear. Splines generally are double stubbed as to addendums and dedendums. The addendum of a spline in about .5/DP and the dedendum roughly .625/DP while a gear would have 1.00/DP and 1.25/DP addendum and dedendum.