What is the word or phrase that describes weight of fuel to total vehicle plus fuel?

There isn't one single universally accepted term for the ratio of fuel weight to the total weight of a vehicle plus fuel. However, the most descriptive and easily understood phrases would be:

* Fuel-to-total-weight ratio: This is clear and unambiguous.

* Fuel fraction: This is more concise, and implies a ratio expressed as a fraction or percentage.

While terms like "fuel load fraction" or "fuel weight percentage" might be used in specific contexts, the first two options are generally preferred for their clarity.