Le $TICK, c'est quoi ?

The $TICK indicator is a short term trading indicator.

In a nutshell, the $TICK tells you the number of stocks on the NYSE that are increasing in price versus those that are decreasing in price compared to the previous price quote. In other words, stocks trading on upticks minus downticks.

In other words : "It's the RPM gauge of the market."

Here's an example:
If there are 1200 stocks in the NYSE that are upticking and 400 downticking, you will see a TICK reading of +800.