In terms of the acronym smart what does it mean when a goal is a measurable

In the acronym SMART, M, measurable, means that the goal is achievable and measurable within the time you are given, as well as specific. For example, if you wanted to save up for a trip in x amount of months, your goal should include the number of months as well as how much you want to save. Another example: if you have gotten an F in your Spanish class and you say that you "want a better grade by the end of the year," you have to measure it better. Meaning, what does "a better grade" mean to you? Is it a D, C, B, or an A? You must be able to measure your success.