Burping (belching) means expelling of the air or other gases from your stomach through your mouth. Many healthy people expel some non-smelling air after eating or drinking. Various health disorders can causes excessive burping.
The smell of sulfur (sulphur) or rotten egg burps comes from hydrogen sulfide (H2S), a gas originating from sulfur-containing proteins in certain foods (see below) after they are broken down in the stomach or small intestine by sulfur-reducing microbes. These microbes may be normal intestinal bacteria or pathogenic bacteria.