Object–relational impedance mismatch

Object–relational impedance mismatch means that when you put data into a computer (like putting food into a container), the way it is organized can be a bit different. The way a computer organizes data (in a way called a relational database) is very different from the way a person organizes data (in a way called an object). When you try to put data from one kind of way into the other, it doesn't always fit very well and this causes problems.