What is the definition or description of: anti-reflux surgery?

Reduces reflux: A surgical intervention to reduce gastroesophageal reflux (reflux of stomach juices into the esophagus - gerd). Gerd can lead to ulcers and possibly cancer of the esophagus. In cases of severe gerd surgery is the current standard, and is mostly performed as a laparoscopic "stomach wrap" (fundoplication). There are newer techniques that are performed endoscopically.

Making better valve: ... To keep stomach acid in stomach. I presume you're talking about an operation to prevent or decrease gastroesophageal reflux (ger). The most common anti-reflux operation performed in the us is a fundoplication in which the top of the stomach (fundus) is plicated or wrapped around the bottom of the swallowing tube (esophagus) to make a better valve there. It can either be a full or partial wrap.