Need help understanding thin lenses for progressive?

[optical glasses]

I need someone to help me understand why some progressives have prism thinning. And the cheap prism lenses. What progressive do you recommend or suggest?

[optical glasses]

lol

My optician asked me if I need prism in my lenses when I order eyeglasses last week, what’s prism? I have never heard about that! I have worn out 2 pairs of eyeglasses, and there’s no such prism in my lenses, Why do some progressive lenses need it?