Usually a 20 foot container with built in refrigeration equipment. Can also be 40 and can be 10 foot and can also be a tank-tainer. Fully self contained. They can run out of fuel and become hot boxes. Stuff in them can go bad even while under refrigeration just like in your fridge. They can also be freezer containers. They are handled just like regular shipping containers by cranes, rail, ships and trucks.
Once these boxes lose power, the contents will rapidly spoil. Given sanitary food requirements and similar requirements for pharmaceutical components, these shipping containers will become pretty much total losses once spoilage occurs and require either scrapping or decontamination and total rebuild
Best to off load and either sell or distribute locally because otherwise you will have too off load and dispose of contents. Once the goods spoil the container is made totally unusable so if the contents are left to rot we will see a major shortage of shipping containers because the contaminated containers will need to be condemned