A million shares a day at 2 is two million dollars — very little. A hundred thousand shares at 300 is thirty million — plenty. Always measure in money. A common working threshold: above ten million dollars a day for intraday, above twenty for meaningful swing size.

The spread is the gap between the highest bid and the lowest ask. In a liquid name it's a cent; in a dormant one it can be a full percent, meaning you're down a percent the instant you enter. Slippage is the gap between the price you expected and the price you actually got, and it grows as your position grows relative to turnover.

Rule of thumb: once your position exceeds about one percent of average daily turnover, you are moving your own price — first on the way in, and worse, on the way out under pressure.

Float is the share count actually available to trade, excluding insider and founder holdings. A small float meeting big volume produces violent moves both ways, which demands a much smaller position, a wider stop, and the acceptance that opening gaps can jump over it.