What does A x B mean when referring to wire strand count?
Vicatcu is right, the first number, being 19 is clearly the strand count. Common stand counts are 7, 10, 19, 26, 41, 65. 

The second number is the gauge of each strand. If you look up a table of AWG wire sizes, you'll see that 20 gauge wire has a cross sectional area of 0.518mm2, making a total cross sectional area of 19*0.518 = 9.842mm2. AWG 16 has a cross sectional area of 1.31mm2.

Therefore I conclude that you mistyped the number. Perhaps you meant 19/29? AWG 29 is 0.0642mm2. 19 of those makes up 1.22mm2, which is very close to AWG 16.

I more often see the strands specified with a / rather than a x. E.G. 19/29.

Looking at a chart of available stranded wires, I see that 19/20 is an offered size.