A person with whom you are insufficiently acquainted to either make easy small talk or enjoy a comfortable silence. An "awkwaintance" is often the friend of a friend; he or she is promoted to the position of "awkwaintance" when the mutual friend leaves you two alone.
(Ash and Gary are at dinner. Brock walks up.)
Ash: Oh, hey, it's Brock! What's going on, man! This is Gary; Gary, Brock. Join us, Brock!
(10 minutes later.)
Ash: Sorry, I have to go be somewhere by myself for an unspecified length of time. Later, guys!
(Gary and Brock, newly made awkwaintances, finish their meals in uncomfortable silence, punctuated by disjointed small talk and uneasy chuckling.)