A partial basement typically means one that is used for storage, hot water heater, washer and dryer, etc......A utility room basically. It needs ventilation if you use it for those purposes though.
A partial basement is usually one that doesn't cover the entire house. Like The Back 40 said, these are typically used for hot water heaters, furnaces, washers and dryers, or for storage.
A partial basement can also be one that isn't fully finished.