Proc is a term that has several meanings "Programmed Random OCcurence" is one, "Process" and "Procedure" are other examples--which typically comes from abilities that have a random chance of occuring on each raid hit.
To figure out how much damage an ability with a damage proc. Find the mount in the list (first post) and multiply the ability's % damage (for 1 stam/honor) by the proc rate (remember that 11.2% would be .112). This will give you the average damage % that ability will give you over many hits, if you multiply it by your actual average damage per 1 stam/honor, you could add it to the AV*4 figure for the mount's full power.
The Rock Worm's ability causes 26% damage at a 22.3% rate (first thread currently shows 24% but it hasn't been updated to reflect an additional 500 hits reported), so (.26*.223)=.058, or 5.8% average increase to your damage. As an example lets say that your average damage per 1 stam is 6000 (would be 123,000 per 20-stam hit) so (.058*6000)=348 average damage added per 1 stam hit. Add that to the AV*4 for Rock Worm (110+348)=458 total damage.
Crit is a proc that increases the damage by 100%. Simply take the critical increase rate (careful to take the 2nd figure listed; since the first includes the natural crit rate) as the average damage increase over time.
The Griffin's ability causes an 8.53% increase in crit rate. Since crit is 100% increase to damage (which means we multiply the rate by 1, so no change) we recognize that it is 8.53% average increase to your damage. Taking the 6000 average regular damage again, (.0853*6000)=511.8 damage added per 1 stam hit. Add that to the AV*4 for Griffin (135+512)=647 total damage. So we see that the Griffin does 189 damage on average more than the Rock Worm for single stam/honor hits.