A consecrated host is a Eucharist wafer which has been ritually blessed by a Catholic priest as part of the Eucharist ceremony. After each cracker is blessed, the priest gives it to a parishioner who is then expected to consume it before returning to her/his seat. It is not clear if this expectation is doctrinal or merely customary, and adherence to it varies.
Catholic doctrine holds that consecration somehow converts or transforms the Eucharist wafer into the "Body of Christ", but that there is no way to detect this change (i.e. to tell whether or not a given cracker has been "transubstantiated").
The transformation involves a concept which doctrine refers to as the "substance" of the wafer -- a misleading label, as the physical properties (substance) of the cracker are not altered. It is unclear why Catholics believe that any change has taken place, as nobody has ever demonstrated such change or even described what the effects of such a change might be. The claim of transubstantiation is therefore non-falsifiable.
Further, the doctrine apparently leads to the conclusion that improper treatment of the cracker is somehow harmful to Jesus Christ – even when such improper treatment merely involves not eating the cracker, or even merely delaying such consumption until after returning to one's seat (see 2008 sacred wafer scandal).
Despite official doctrine, however, many Catholics believe (in accordance with common sense) that the transformation is meant to be purely metaphorical, and that improper handling of the wafer is a minor social crime (on the approximate order of littering or burping loudly in a quiet room); taking the cracker back to one's seat before eating it is a widespread practice among Catholics.
As of 2011-08-17, none of these reference works contains an article dedicated to this subject: