What is the difference between a Splitter and a Tap ?

A tap (a.k.a. directional coupler) has one input, and two output legs, usually labeled "TAP" and "OUT". The TAP leg incurs -6db loss, while the OUT leg incurs very small (~-1db) loss.
Taps are used when a cable needs to keep the signal as clean as possible on one leg (to continue to feed TVs/modems on it downstream), while the other leg is to be terminated close to the tap, or loss on it is not crucial.

Splitters commonly incur the same amount of insertion loss on all output legs.
2-way splitter incurs -3.5db signal degradation on each leg.
3-way balanced splitter incurs ~5.5db-6.5db on all legs. (there is an "unbalanced" variety that has -3.5db loss on one leg, and -7db on the other two, similarly to using two 2-way splitters).
4-way splitter will cut -7db on all legs.
8-way splitter has -11db loss on each leg, and so on.

Taps are sometimes preferred to splitters if you need a cleaner signal to a cable modem (connected to the "OUT" leg of a tap), while connecting TVs to the lossy "TAP" leg of the tap.

Keep in mind that splitters introduce loss in the return/upstream direction as well.