Mid-Cap

It's the size of the companies a typical mutual or index fund might invest in.

Like...you have the mega-cap companies like Amazon and Apple and Google, all worth half a trillion bucks or more. Then you have the micro and small cap companies valued under a billion bucks.

So what's the size of a mid-cap? Well, there's no set number, but most larger Wall Street firms think of mid-caps these days as being valued somewhere between $10 and $100 billion. They're stable and secure-ish in their markets, so they're not going to evaporate in a few years. But they're also not growing super fast like their tiny brethren in the small cap world. They're also not fighting the law of large numbers of the mega caps, which already own all of their markets and just hope the markets grow.

And remember the valuation of these companies: number of shares outstanding times stock price. So if you have a company with a billion shares out, which is trading for $25 a share, then that's a mid cap, valued at $25 billion.

See: Market Capitalization.