Mathematical Sans-serif Bold Small D (U+1D5F1) is a Unicode lowercase letter from the Mathematical Alphanumeric Symbols block. It resides on Plane 1 (SMP, Supplementary Multilingual Plane), has bidirectional class L (left-to-right), is not mirrored, and has combining class 0 (Not Reordered). In HTML it can be written as 𝗱 or 𝗱. Because it is outside the Basic Multilingual Plane, proper font support is required; otherwise a fallback box may be shown.