Total traffic is a metric pulled from SEMrush that estimates the total traffic that your website gets based on your keyword rankings. It is estimated based on the average keyword ranking position and the average click through rate (CTR) based on that search query.
Although this is not an absolute metric, SEMrush's estimations are consistent across all domains, and therefore can be a great comparison tool to analyze differences in traffic between your website and your competitors.
It is also a great benchmark for discoverability, because as your estimated total traffic increases your discoverability on the internet increases and your top 20 keyword rankings most likely increased as well.
With Pulse, you are able to track changes in total traffic over time, and benchmark these changes with your competitors.