Wide data describes a structure in which a measure in a single row is spread over multiple columns. This data is often more human readable. Wide data often results in fewer rows with more columns.

Here is an example of what wide data looks like in a table of population numbers:

Notice that the level of detail for this table is a row for every country. However, the single measure (population) is not stored in a single column. This data is wide because it has a single measure (population) that is being divided into multiple columns (a column for each year). The wide table violates the second key of good structure since the measure is at a lower level of detail than the individual record (per country per year, instead of just per country).