Here are some terms I use regularly, and some descriptions of how they are calculated. This is so I don't need to keep explaining them in every post.
Activity Rate measures how quickly a batsman scores their runs off deliveries that they have not hit to the boundary.
The formula for it is (run runs)/(balls faced - boundaries hit). Run runs is all runs that are not from boundaries, so it includes any incidence of 4 over-throws. This is for two reasons. Firstly 4 overthrows is often a reward for batsmen taking on the field, and as such it is related to them being active and looking for runs. Secondly it's really hard to remove overthrow boundaries, without searching through ball by ball reports of individual innings.
Batting Index/Bowling Index.
Batting/Bowling Index combines average and strike rate.
I feel this is the most useful way of comparing batsmen, and a reasonably good way of comparing bowlers. The formula is Batting: (runs^2)/(balls faced * dismissals) and Bowling: (runs conceded)^2/(balls bowled * wickets taken).
This also allows us to compare players from different eras. For example we can compare Kallis, who scored at an average of 45 and a strike rate of 73 (batting index about 33) with Glen Turner who scored at 47 and a strike rate of 68 (batting index of about 32). Whereas it is not really fair to compare their averages or strike rates as the times they played in were quite different.
This is the players average (either batting or bowling) up to that point. For example while Don Bradman's career average was 99.94, after two matches he had scored 210 runs in 4 innings and so had a cumulative average of 52.50.
This is the average for a player over 15 innings, recorded at the 8th innings. It is the average of that innings as well as the 7 innings before and the 7 innings afterwards. It's used as an indication of form.