Where is the variable named 'model' which is passed to fit() function?

Why is this model keyword used here in the code but there is no any variable named as model in the entire code

def fit_v2(x, y, model, opt, loss_fn, epochs = 2000):
    loss_arr = []
    acc_arr = []
    for epochs in range(epochs):
        loss = loss_fn(model(x), y)
        loss.backward()
        opt.step()
        opt.zero_grad()
    return loss.item()

See, its used for building argument for loss_fun