Best effort is an expression used to describe a level of effort that is the most that can be done in a given situation. It is often used to describe a person's attempt at a task or goal, and implies that they have done their best with the resources available. The crossword solutions for the term BEST EFFORT are ALL, which stands for 'all out' or 'all-out effort'. This means that the person has put in their maximum effort in order to achieve the desired result.