Curve Distribute Between UVs

Default Options

With the default options, "Curve Distribute Between UVs" will distribute UVs forming path between your selected UVs along a (dynamically created and not retained) NURBS curve passing between the UVs you've selected:

Note: The UVs selected adhere to the same logic as Select UVs Between UVs.

Proportional Distribution

The default distribution type for this tool is "Uniform", however you can select "Proportional" distribution in order to distribute UVs with spacing relative to their distribution in 3d space:

Use Selection Order

If your selected UVs form a path with multiple directional changes, you'll want to check the "Use Selection Order" option for the most predictable results:

Close the Loop

If you want the curve along which your UVs are distributed to form a closed loop, you must have selected "Use Selection Order", and "Close":