format: what is loose anc compact?

[Francesco Potorti`]

In the 'format' help string I read:

    `compact'
          Remove extra blank space around column number labels.

    `loose'
          Insert blank lines above and below column number labels (this
          is the default).

but I do not know what are "column number labels", nor do I see any
difference when trying these.

What do they mean?

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