Reflux (noun)

1. The flow of a liquid back into a container from which it has overflowed or from which it has been poured.
2. The backward flow of a liquid, especially gastric juice, from the stomach into the food pipe.

Origin:

Late 19th century: from latin refluxus, from re- 'back' + fluxus 'a flowing'.

Examples:

1. The reflux of water from the tank into the pipe was caused by a blockage in the pipe.
2. The reflux of acid from the stomach into the esophagus caused heartburn and discomfort.
3. The reflux of oil from the tank was due to a valve malfunction.
4. The reflux of the mixture into the flask was prevented by a condenser.
5. The reflux of the solvent into the reactor was regulated by a control valve.