Market Capitalization (or 'Market Cap') is the fundamental way to measure how much a publicly traded company is worth on the stock market. It tells you exactly what it would cost to buy every single share of the company.
Investors use market cap to categorize companies. 'Large-cap' companies are usually valued over $10 billion (e.g., Apple, Microsoft). 'Mid-cap' companies are between $2 billion and $10 billion. 'Small-cap' companies are valued between $250 million and $2 billion.
Understanding market cap is crucial because large-cap stocks tend to offer stability and dividends, whereas small-cap stocks are generally much more volatile but offer higher potential for rapid growth.