DeCap is short decoupling capacitor. DeCap is nothing more than another name for bypass capacitors, which are capacitors that typically are connected between a supply and ground or between two supplies that provides an alternative path (a bypass) for high frequency currents in attempt to keep these currents away from the power supply to reduce noise coupling through the supplies.

Bypass is the less ambiguous of the two terms, as there is natural confusion between coupling & decoupling capacitors. A capacitor that is connected in series acts to pass (couple) high frequency signals while blocking (decoupling) low frequency or DC signals. There are also decoupling inductors, which would sit in series with the supply and work with bypass capacitors to block tranmission of noise currents between loads. (see http://designers-guide.org/Design/bypassing.pdf).

While there is ambiguity between coupling and decoupling capacitors, the term decap almost always refers to bypass capacitors.

I recommend that you continue to use the term "bypass capacitor" because it is more descriptive of how it really works, and because it is less confusing.

-Ken