TITLE: What is "topology in dimension 3.5"?
QUESTION [7 upvotes]: I've noticed a couple of conference titles which reference something called 
"topology in dimension 3.5," such as this one and this one. This subject seems quite mysterious to me — it looks like it's part of geometric topology, but I'm guessing it's not about 3.5-dimensional manifolds, so what kinds of things are studied in 3.5-dimensional topology?

REPLY [4 votes]: cw answer: As mentioned in the comments, this just refers to the relations between 3-dimensional and 4-dimensional topology.