A potentially incorrect but reactionary belief is that a pavilion may not be intended for continuous occupation enabling work or living.  They might not be enclosed enough and/or climate-controlled to the extent to make that possible.

contemporarily....

a 'typical' building is built for a function beyond itself

a pavilion is built for the function to present itself as a function of a patron idea/theme (nationalist, industrialist...).

the former does not act, typically, as an intermediary agent of reference. it is in ready-to-hand (to use a heideggerian term) state of architecture. its function normalizes it.

the latter's intention is to do so. so it is an intermediary intra-referential agent of an extra-reference and simultaneously it is an estranged instance of architecture  in an abstracted state of presence-at-hand.

however, the divide may only be a matter of tendency. as an example of that, zaha hadid (oop)'s vitra fire station lost (or may never had been invested much in) its initial tendency towards the state of a normalizing function (as a fire station) in favour for the tendency towards self exibition, a pavilion.

in many seminal buildings (for example mies' towers or le corbusier's houses) the buildings exhibit both tendencies.

it is interesting that a pavilion, referring to itself (denotation) and hence to an external reference (connotation) should also occuppy such an embryonic semiotic space. to draw parallels with freudian though, it has not formed normative relationship with the world through a mature societal function but is in a solipsistic state of auto-eroticism. an onanistic architecture?   

an onanistic architecture?  

And I'm called on the carpet for being verbose?  That was very elegant, but I didn't understand much of it at all.  I can deduce you are in the UK, or one of its former colonies, where they spell favor "favour."

The hyphenated is all I understood.  Onanistic = onanism = masturbation.

^ Not hyphenated - s/b italicized

actually, you may ask what extra-referential purpose does/did hadid's vitra fire station serve, to criticize me for the above. that came to mind while showering, i put a small trap for myself.

but not really...i should not subtract but rather add. a pavilion -as we architects understand it in its capacity to fulfill an a(A)rchitectural purpose- also has yet another, a third level of reference relating the pavilion/ small "a" architecture to a capitalized "A" Architecture. the architecture contains within itself the kernel of Architecture, a specific embryonic manifest/manifesto thereof.

so, although the vitra fire station does not have an extra-thematic reference (it does not signify a country or an industry and so on in any form) , it did signify a new generation of design work and a new synthesis of forms and ideas, a promise of more to come. poetically that it was also, in form, dynamic. so, yes, i consider it a pavilion and i consider that level that relates a pavilion to the culture of Architecture as more important and significant (being more interested in design than in associatively referential political posturings) than its referential function in relation to the patron theme/idea. as an example, the barcelona pavilion outgrew any nationalistic patronage. it is, simply, one of the most iconic modernist architectural works irrespective of country of origin and it even outgrew its original architectural being (its architectural clone took its place - an example of Architecture superceding architecture).

observant, i am not from a former british colony. favour is a default spelling (having been around a wee bit longer).  if i write "favour", that would not be so much a matter of deliberate choice. if as "favor",  then it very much would be so for me. perhaps the english taught in latin american countries favours "favor" as its default being that they're so much closer to the US?  

^ word salad

with thousand island dressing