These are text files that describe binary data.
In their simplest form, they contain only the minumum information needed by DDS to access binary samples.
data=vel_z6.25m_x12.5m_exact.segy
format=segy
axis= z x y
size.z= 1911   size.x=5395   size.y=1
delta.z= 6.25  delta.x=12.5  delta.y=12.5
origin.z=0.0   origin.x=0.0  origin.y=0.0
units.z=m      units.x=m     units.y=m
Definitions in this dictionary are given by name= value.

format=segy is a complete definition. White space is not allowed before the "=" sign, but is allowed after it. More than one definition can be given on a single line and definitions can span more than one line.

A more complete description is available under the Users -> Definitions tab.