Loss of life (also reffered to as "Loss of HP" & LoL) is an effect which reduces a champion's current HP. As is commonly stated, Loss of life is not considered to be damage, despite reducing HP & appearing similar in the interface. This means abilities such as Drive are separate from any ability/condition which mentions "damage". For example, loss of life does not get reduced by Impervious.
Loss of life will bypass all clauses that use the term damage as a trigger .
Deflect and Impervious are both abilities that use "damage" as a trigger for the abillity to take effect. Thus, LoL damage will not trigger these abilities.
Loss of life damage does not currently bypass defense . Defense currently reduces all sources of HP reduction, that lack a clause bypassing it.
Loss of Life Sources