Glossary
Tap
In one line: Firing one shot at a time, calmly, for maximum accuracy.
What it means
A tap is a single shot: click once, wait for your accuracy to reset, click again. It is the most accurate way to shoot, so it is used at long range and with guns built for it (Sheriff, Guardian, Vandal at range).
With the Vandal and a few other guns, one headshot kills an armored enemy at any range: that is why at distance a good tap beats any spray. Tapping takes patience and good crosshair placement.
An example
An enemy crosses the far end of a long corridor. With the Vandal you do not hold the trigger: one tap to the head and they drop. Had you sprayed, your bullets would have scattered all around them.