What is the difference between long and wide format?

In wide format, all the features of an instance are provided in a single row with each feature being indicated in separate columns whereas, in the long format, a particular instance is repeated in each row with different attributes, i.e. in the long format, only one attribute is specified in one row. The following tables are examples of long and wide formats:

Name Age Blood Group
Siddhartha 23 AB+
Sahil 22 A-

                                                                                Wide Format

Name Attribute Value
Siddhartha Age 23
Siddhartha Blood Group AB+
Sahil Age 22
Sahil Blood Group A-

                                                                                  Long Format