Productivity means different things in different contexts. The easiest way to see productivity is in something like a factory where they produce things. But in many fields productivity can be how much value you're extracting, i.e. how much money is this industry making. The assumption is, if you are charging X amount for something and people are actually buying it, it must be worth that much. This assumption is based on really old economic theory where if something is overpriced people wouldn't buy it and they'd be forced to make it cheaper to reach market equilibrium.

Another measure of productivity can be growth. We generally measure the growth of the economy based on money and jobs. How many jobs has this industry added, which can indicate they are producing more.

TLDR; To simplify, productivity can be a tier list. Are you producing more? You're being more productive. Are you making more money? You're being more productive. Are you adding more jobs? You're being more productive.