I work for a medical device/pharma company. For us, the expiration date is based on the period of time that we have data to provide evidence that the material is stable or sterile. Chemical change over time, please be aware of the dates on your medications and drug products (even cosmetics have dates, bacteria grows on/in open items).
Food dates are a little different, there are normally sell by and use by. If you have not used it by the use by, I might use it If it was being fully cooked and it smelled normal. When in doubt, toss it for your safety.