Measures of Central Tendency
Average could mean one of four things. The arithmetic mean, the median, midrange, or mode. For this reason, it is better to specify which average you're talking about.
This is what people usually intend when they say "average"
The mean of a frequency distribution is also the weighted mean.
The mode is the most frequent data value. There may be no mode if no one value appears more than any other. There may also be two modes (bimodal), three modes (trimodal), or more than three modes (multi-modal).
For grouped frequency distributions, the modal class is the class with the largest frequency.
The midrange is simply the midpoint between the highest and lowest values.