They are called "Throw back's".  Each team will wear old uniforms every so often.

Like most teams nowadays, the Jets like to play at least one home game per year in their old, original uniforms.  It is weird to be the game, and see your guys wearing uniforms whose closest analogy is the Rams.  Then again, the Jets have never lost a game in those uniforms to date, so I have no problem with that...kinda cool, in fact!