Bid Tick

A typical retail trader (a regular person just making a few transactions here and there on their lunch break) will likely follow a stock by looking at the price posted on mainstream stock-tracking websites, making any investment decisions from there. Professional traders go a little deeper.

Behind a stock's price, there's an intricate auction system of bid and ask. Bids represent orders to buy a stock and asks represent orders to sell (See: Bid and Asked). Tracking a bid tick means tracking the order flow on the bid side of the equation. Each bid tick indicates the movement in the bid price, whether moving higher or lower or holding steady.

A savvy trader can read the trend in the bid tick to garner micro advantages in the stock's movement. These kinds of additional benefits don't mean much for any particular trades (so aren't worth tracking for once-in-a-while types), but the additional value can add up over time if the trader is working in a high-volume environment.