Social proof is evidence that other people use and trust a product: testimonials, user counts, customer logos, reviews, ratings and badges from launch sites.
People decide faster when they see others like them already made the same choice.
Specific proof beats vague proof: a named user with a concrete result is more convincing than "loved by thousands".
Why it matters for a launch
A new product has little of it, so every early testimonial and launch badge is worth collecting and showing.