What is interval

#1
This is what always confuses me about the term [I think they use the word continuous for interval]

"effort: a continuous variable ranging from 0 to 50, which is an average of weekly subject-reported effort scores, also ranging from 0 to 50, with 0 denoting minimal physical effort and 50 denoting maximum effort."

So formally something with only 50 values is not interval. The number of values has to be infinite because you can always divide and thus get more values. But at a certain point if you have enough distinct levels I think it becomes effectively interval [interval like some call it].

Is that true? Or in this case does the fact they average things to get the 50 distinct values make it interval?