The Delta is the point on a ridge at or in front of and nearest the center of the divergence of the type lines. It can be a bifurcation, an abrupt ending ridge, a dot, a short ridge a meeting of two ridges (convergence), or a point on the first recurving ridge located nearest to the center and in front of the divergence of the type lines.
A definition which people may be more familiar with is one of a river; where alluvial land deposit is enclosed within 2 or more mouths of a river, like the delta of the Nile (in the image above).
In terms of friction ridge fingerprints, it is the first ridge or part of a ridge nearest the point of divergence of the 2 type lines. Diverging type lines must be present in all delta formations and the formation akin to the alluvial deposit (ie dot or otherwise), it must be located midway between 2 diverging type lines at or just in front of where they diverge.
The important rule to remember is that the delta must be located at a bifurcation that opens toward the core. Another way of looking at this is where there are 2 or more possible deltas which conform to the definition, the one nearest the core is chosen.
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