Many people use these terms interchangeably! However, a gooseneck and a 5th wheel are not the same thing. While both types of trailers attach to the truck in the truck bed, the way these two attach is significantly different, and they are not interchangeable.
A gooseneck trailer slides over a ball hitch in the bed of a pickup truck.
A fifth wheel trailer attaches to a pickup truck using a hinged plate hitch in the truck bed; the same type of hitch is used by semi trucks.
They do, however, make an adapter so that you can use your trailer with the wrong type of truck hitch. This is not recommended for repeated use, just for one time or emergency hookups. Always install the hitch your trailer is designed to hook up to!
What the 5th wheel adapter for a gooseneck could look like (truck has a 5th wheel, trailer is a gooseneck):
What the gooseneck adapter for a 5th wheel could like (truck has a gooseneck, trailer is a 5th wheel):
A side note: The biggest advantage of a gooseneck or even 5th wheel trailer over a bumper pull is its stability. They also typically can haul a heavier load. They even can feel “lighter” to pull than a bumper pull because of the weight dispersion.