Is attending conferences while teaching considered an absence? Is attending conferences considered an absence? If not, then is there a limit on how many conferences a faculty can attend?!
While I have never experienced a department that defined "absent days", if your department regulates these things, you need to ask you department chair what the policy is.

Departments that I am familiar with expect you to either teach when you are supposed to, arrange someone to cover the teaching, or rearrange the session. In some situations an out of class activity wold be acceptable and in rare cases outright canceling of the class. One should try and keep these to a minimum, but to the extent that the students are not complaining, you can probably get away with it.

I have never seen a department which limits the number of conferences, but if you are rarely around, it will probably come back to bite you. In general, if you are worried about these things, you should ask a senior colleague.