What Does Clerical Mean?

Anything pertaining to the clergy is also known as "clerical." A clergy is a person elected to do religious work. It is a term assigned to leadership within a particular religion. In other words, the ritualistic rites, preaching the religious doctrine and conducting ceremonies like baptism, circumcision, marriage, funeral procedures etc, by following the customs required by the religion are the duties of the clergy or 'clerical duties'.

Working in hospitals, military, and doing missionary work including ritualistic ceremonies, even outside the realm of the place of worship are some of the other clerical duties.  
Simply put, clerical means "office related" A clerk is a person who works in the office. Clerical work would imply office work like filing, documenting information or maintaining records, stationery etc

Clerical is an office position.  Typing, filing, answering phones and misc.  You know all that important stuff that the higher ups need done and have no clue how to do themselves....lol.