x1 is a region/room/volume of space which is shaped like a washer (or thin or flattened torus/toroid), between inner disk/sphere x2 and outer disk/sphere x3, defined by midplane x4, and containing x5.
x1 canlu. This word contrasts with "torxesu" in that, while neither is necessarily a material object, this is a region of space and not an idealized object per se, and that, while this region is technically three-dimensional, it is mostly considered to be flat or nearly two-dimensional (similar to "karda"). Therefore, it will not take up/fill all of the space between the inner and outer spheres; it is confined approximately to the plane x4. x3 should enclose x2 (except at most one point unless the case be degenerate), but they need not be mutually concentric. x1 need not be perfectly circularly toroidal; for example, it could be elliptical (in which case, x2 or x3 would not be perfectly spherical either). Contrast with "bolbi'i", which is the whole region between the spheres x2 and x3 when this word makes sense, but which also does not require the nesting of the said spheres. This word is a brapagjvo; see: "jinrcaiba", "belta". Consider just using either "djine" (for an object) or "jinca'u" (for a region of space).