Is this a floor framing system? what is the difference between joist splices and floor joists?
Joists are just that, members that carry the sub-flooring or ceiling. A joist splicing occurs where the length of span of the floor is longer than the joists are capable of supporting so a beam or "girder" is placed under the ends of the joists. Joists from either side of the support beam overhang the beam some and overlap with their companion coming from the other side. This picture shows the concept:



Picture Source