The thickness of wire is rated by gauge (ga), with 00 being the largest, and 36 being ultra-thin. If the wire is composed of a single solid core, then its rating is its thickness, period.
However, if the wire is stranded, it can be specified by its overall thickness (most common in hardware store), or it can be specified by the thickness of each strand multiplied by the number of strands.
So 105x36ga is a finer stranded wire than 26-30ga.
In the high end audio world, there is some disagreement over the virtues of stranded wire vs solid wire based upon effects according to electrical theory, shouldn't make a difference. I don't think there's a difference in sound between solid, stranded, or ultra-thin stranded.
In general, solid cord wiring is used in permanant installations (such as home wiring), and more expensive stranded wiring is used in vehicles and airplanes where vibrations and sharp bends might eventually cause fatigue failures in solid wires. The finer the strands, the more flexible and soft the wire usually is, though that's also a function of what material they use for insulation.