Two related options here: Trim sheet = a bunch of textures laid out side-by-side inside one bitmap. Decal sheet = same, except these are overlaid on top of another texture. Either via transparent edges, or buffered rendering (deferred rendering, stencil buffers, etc.).
@lockey1995 The most optimal way would be trim sheets for a staircase, yes, since there is plenty of repeating elements. What you referred to in the first post, the sheet with tons of different details that don't flow together, is known as a decal sheet. Which can be used to just float details onto meshes.