Hose Barb Nipple.
This fitting is used simply to connect two lengths of hose together in a "non-disconnectable" fashion. That is, unlike a threaded connection, which can be disconnected with a wrench, this connection is "semi-permanent", in that disconnecting or "un-doing" the connection is non-trivial, requiring tools and possibly trimming of the hose ends.
[1]
[2]