Market capitalization is the total cash-value of a business. AKA market cap. The market cap is calculated by multiplying the current number of shares outstanding by the price of one share. For example, a company having 1000 shares of 10$ value would have a market cap of 10,000$.
Companies are usually classified based on their market as small-cap, large-cap etc. Microcap refers to a companies that have much smaller capitalizations. In the U.S. it refers to companies having a market cap of roughly 50-300M$.
Microcap companies are not that popular. And not that well.covered by mainstream media. Hence the volumes traded on these stocks are quite low. This can be risky as it might be hard to offload or buy into large positions.
Since the companies are not that well-covered, the data on these companies are generally good. Less noise overall. And these companies are usually easier to analyse as they have simpler businesses and product lines compared to larger companies.