I consider a bubbler to be a pipe with a water feature and a pipe style mouthpiece. A bong is usually bigger and has a wider mouthpiece as compared to a bubbler.
• Bongs are water pipes and operate upon the same principle as hookahs in many eastern countries for centuries • Bubblers are similar to bongs except that they are very small in size and can be operated with a single hand by the smoker • The internal water chamber in bubbler is very small and hence needs frequent cleaning unlike bongs that are large in size • Bubblers are cheaper than bongs •Younger people prefer bubblers because of their compact size as they can be carried and hidden easily
I once had a bubbler that was about 15 inches tall. It was a kind creations piece, felt like a bong to me but they called it a bubbler. I miss that piece