?? About 1955 Topps

I'm working on a 1955 low grade set and notice several cards are denoted DP. Which I assume means "double print", correct? What does "double print" mean? I have seen this denotion since I have been collecting but, never understood the meaning.
EX:
172 - Frank Baumholtz DP
Thanks, David
EX:
172 - Frank Baumholtz DP
Thanks, David
0
Comments
With regards to the 55's, while #172 is a DP, remember that it is a DP in the higher number series, so while it is twice as plentiful as other cards from the same series, it is still rarer than cards in the low number series.
Always looking for Mantle cards such as Stahl Meyer, 1954 Dan Dee, 1959 Bazooka, 1960 Post, 1952 Star Cal Decal, 1952 Tip Top Bread Labels, 1953-54 Briggs Meat, and other Topps, Bowman, and oddball Mantles.