What is the difference between moha (delusion) and avijja (ignorance)? What is moha (delusion)? What is avijja or avidya (ignorance)?

What is the difference between moha (delusion) and avijja or avidya (ignorance)?
I think it requires a lot of research or another's excellent research to answer this question. 

Often ignorance &amp; delusion are used as synonyms, for example, as follows: 


  Bhikkhus, I do not perceive any single hindrance other than the hindrance of ignorance by which humankind is so obstructed and for so
  long a time runs on and wanders in saṃsāra. It is indeed through the
  hindrance of ignorance that humankind is obstructed and for a long
  time runs on and wanders in saṃsāra.
  
  No other single thing exists Like the hindrance of delusion, Which so obstructs humankind And makes it wander on forever.
  
  Those who have abandoned delusion, Cleaving through this mass of darkness, No longer roam and wander on; In them the cause is found no
  more.
  
  Iti 14
  
  
  
  Bhikkhus, any bhikkhu or bhikkhunī in whom attachment is not abandoned, hate is not abandoned, and delusion is not abandoned, is
  said to be one who has not crossed the ocean. One who has destroyed
  attachment Along with hate and ignorance Has crossed this ocean With
  its sharks and demons, Its fearful waves so hard to cross.
  
  Iti 3.69


However, I imagine 'ignorance' ('avijja') literally means an underlying 'lack of knowledge' or 'blindess'; where as 'moha' ('delusion') literally refers to the defiled overt manifestations of that lack of knowledge, such as 'self-view', 'selfishness', 'ingratitude'; 'fear', 'doubt', etc. 


  Humankind is possessed by delusion, Bound by delusion and delighted with being
  
  Iti 1.11 Mohapariññā Sutta
  
  
  
  Delusion is that one thing, bhikkhus. Abandon that and I guarantee you non-returning. Beings confused by delusion Go to rebirth in a bad
  bourn. But having rightly understood delusion, Those with insight
  abandon it. By abandoning it they never come Back to this world
  again.
  
  Iti 1.3 Moha Sutta


From the viewpoint of Dependent Origination, 'delusion' would be a type of craving (8th condition) leading to attachment (9th condition) that propels wrong action; for example:


  It’s not because of deeds born of greed, hate and delusion that gods, humans, or those in any other good places are found. Rather, it’s
  because of deeds born of greed, hate and delusion that hell, the
  animal realm, the ghost realm, or any other bad places are found...
  These are three sources that give rise to deeds.
  
  AN 6.39
  
  
  
  Killing living beings is unwholesome; taking what is not given is unwholesome; misconduct in sensual pleasures is unwholesome; false
  speech is unwholesome; malicious speech is unwholesome; harsh speech
  is unwholesome; gossip is unwholesome; covetousness is unwholesome;
  ill will is unwholesome; wrong view is unwholesome. This is called the
  unwholesome.
  
  And what is the root of the unwholesome? Greed is a root of the unwholesome; hate is a root of the unwholesome; delusion is a root of
  the unwholesome. This is called the root of the unwholesome.
  
  MN 9
  
  
  
  A deluded person, his mind bound up, overcome with delusion, engages in bodily misconduct, in verbal misconduct, in mental misconduct. But
  having abandoned delusion, he doesn’t engage in bodily misconduct, in
  verbal misconduct, or in mental misconduct.
  
  AN 3.71


Therefore, it appears 'delusion' (such as 'selfishness') is a form of craving &amp; attachment that manifests abruptly and overtly &amp; then calms down; where as 'ignorance' (lack of knowledge) is a more permanent underlying tendency (anusaya) in the unenlightened mind.


  Friends, passion carries little blame and is slow to fade. Aversion carries great blame and is quick to fade. Delusion carries great blame
  and is slow to fade.
  
  [Then if they ask,] ‘But what, friends, is the reason, what the cause, why unarisen passion arises, or arisen passion tends to growth
  &amp; abundance?’ ‘The theme of the attractive,’ it should be said. ‘For
  one who attends inappropriately to the theme of the attractive,
  unarisen passion arises and arisen passion tends to growth &amp;
  abundance…’
  
  [Then if they ask,] ‘But what, friends, is the reason, what the cause, why unarisen aversion arises, or arisen aversion tends to
  growth &amp; abundance?’ ‘The theme of irritation,’ it should be said.
  ‘For one who attends inappropriately to the theme of irritation,
  unarisen aversion arises and arisen aversion tends to growth &amp;
  abundance…’
  
  [Then if they ask,] ‘But what, friends, is the reason, what the cause, why unarisen delusion arises, or arisen delusion tends to
  growth &amp; abundance?’ ‘Inappropriate attention,’ it should be said.
  ‘For one who attends inappropriately, unarisen delusion arises and
  arisen delusion tends to growth &amp; abundance…’
  
  AN 3.68


In summary, there are differing degrees of defilements on the Dhamma, namely: 


Anusaya - underlying tendencies 
Asava - outflows; fermentations; cankers; eruptions 
Nivarana - internal hindrances 
Tanha &amp; upakkilesa - external orientated craving &amp; defilements that directly cause action


Ignorance predominates on the subtle degree of 'anusaya' where as 'delusion' predominates at the coarser degree of strong external defilements.