Exchange 2010 what are active sync hits

How many users/devices and how many CAS servers do you have?
What kind of devices? Many questions before anyone can answer.

I was just looking for an explanation of hits. Is hits the number of times an active sync device connects to active sync per day?

To address your question believe it or not

7,000 users
4800 devices--some users have 2-3 and up to 5 in extreme cases.
3 CAS servers but they are all multi-role MB,CAS, HT.
The devices range let me put it like this. This is the worse case of BYOD. Iphone mostly IOS 7 but some IOS6.01 which I already know needs updating (100) of these and the rest are 6.2 IOS and higher. We also have a lot of Driod phones. Some motorola, samsung etc//

Hits are requests made by those devices. If you see that your servers are being taxed too heavily then I would suggest you enforce a throttling policy to keep those users from overwhelming your servers.

http://technet.microsoft.com/en-us/library/dd297964(v=exchg.141).aspx

So my question would be first is. Are hits are defined to be requests made by those devices? What kind of requests? Requests to get data? requests to login? requests? Also what parameter would I use to enfore a throttling to control hits on an exchange server.  I did not catch the post above.