Why is a slash added at the end of the url?

Question

Node.js

Why is there a slash at the end of the url?
http://localhost:3000/auth/create/

auth.js

// Create new account page
router.get('/create', (req, res) => {
  res.render('create-page');
})

app.js

// sign in/up
app.use('/auth/', routes.auth);