A spline is a narrow strip in this case 1/4 in X 1in strip od plywood that is
fitted into a 1/4 in slot cut into each edge of ajoning sheets of plywood
floor hopefully you have axcess to a router and a sloot cutter bit to cut the
groves. the spline can eather be glued in place or left to float(un glued) It
fills the crack and keeps both sheets of plywood eaven with each other.
Hope this answeres your question.
Jim Smith & Little Hemroid(the Spitz pup)