its a defect in the abdominal wall that usually holds back whats inside (could be intestines, fat, or other internal organs) the hole may become bigger letting more out, but it also runs the risk that something (say intestines) can push out and have the blood supply to them cut off which then becomes serious(and needs
surgery ASAP)... but some people may have a
hernia their whole entire lives and live with them with no complications...