Misheel or MishDee is a reference to the relationship between Misha Collins and Danneel Ackles used either as short-hand to indicate the friendship between the, or referring to a fictional relationship in fanfiction or in some fans' heads.
While they have rarely been seen in public together, Danneel appeared in an episode of Misha's web series TSA America: Level Orange and is also on the board of Random Acts. They appeared in three episodes of Supernatural 13.13 Devil's Bargainm 14.17 Game Night and 15.13 Destiny's Child.
Danneel has been known to say that Castiel is her favorite character here at the 300th episode red carpet where she said: "I know all of Cas' lines because he is my favorite. And everybody knows that including my husband!"